diff --git a/mysql-test/r/type_timestamp.result b/mysql-test/r/type_timestamp.result
index 752a5045eb0..6253fa96ba8 100644
--- a/mysql-test/r/type_timestamp.result
+++ b/mysql-test/r/type_timestamp.result
@@ -122,40 +122,41 @@ t2	t4	t6	t8	t10	t12	t14
 0000-00-00 00:00:00	0000-00-00 00:00:00	0000-00-00 00:00:00	0000-00-00 00:00:00	0000-00-00 00:00:00	0000-00-00 00:00:00	0000-00-00 00:00:00
 1997-12-31 23:47:59	1997-12-31 23:47:59	1997-12-31 23:47:59	1997-12-31 23:47:59	1997-12-31 23:47:59	1997-12-31 23:47:59	1997-12-31 23:47:59
 drop table t1;
+set new=0;
 create table t1 (t1 timestamp default '2003-01-01 00:00:00', 
 t2 timestamp default '2003-01-01 00:00:00');
 set TIMESTAMP=1000000000;
 insert into t1 values();
 select * from t1;
 t1	t2
-2001-09-09 04:46:40	2003-01-01 00:00:00
+20010909044640	20030101000000
 show create table t1;
 Table	Create Table
 t1	CREATE TABLE `t1` (
   `t1` timestamp(14) NOT NULL,
-  `t2` timestamp(14) NOT NULL default '2003-01-01 00:00:00'
+  `t2` timestamp(14) NOT NULL default '20030101000000'
 ) TYPE=MyISAM
 show columns from t1;
 Field	Type	Null	Key	Default	Extra
 t1	timestamp(14)	YES		NULL	
-t2	timestamp(14)	YES		2003-01-01 00:00:00	
+t2	timestamp(14)	YES		20030101000000	
 show columns from t1 like 't2';
 Field	Type	Null	Key	Default	Extra
-t2	timestamp(14)	YES		2003-01-01 00:00:00	
+t2	timestamp(14)	YES		20030101000000	
 create table t2 (select * from t1);
 show create table t2;
 Table	Create Table
 t2	CREATE TABLE `t2` (
   `t1` timestamp(14) NOT NULL,
-  `t2` timestamp(14) NOT NULL default '2003-01-01 00:00:00'
+  `t2` timestamp(14) NOT NULL default '20030101000000'
 ) TYPE=MyISAM
 alter table t1 add column t0 timestamp first;
 show create table t1;
 Table	Create Table
 t1	CREATE TABLE `t1` (
   `t0` timestamp(14) NOT NULL,
-  `t1` timestamp(14) NOT NULL default '2003-01-01 00:00:00',
-  `t2` timestamp(14) NOT NULL default '2003-01-01 00:00:00'
+  `t1` timestamp(14) NOT NULL default '20030101000000',
+  `t2` timestamp(14) NOT NULL default '20030101000000'
 ) TYPE=MyISAM
 drop table t1,t2;
 create table t1 (ts1 timestamp, ts2 timestamp);
@@ -164,8 +165,8 @@ insert into t1 values ();
 insert into t1 values (DEFAULT, DEFAULT);
 select * from t1;
 ts1	ts2
-2001-09-09 04:46:40	0000-00-00 00:00:00
-2001-09-09 04:46:40	0000-00-00 00:00:00
+20010909044640	00000000000000
+20010909044640	00000000000000
 drop table t1;
 create table t1 (ts timestamp(19));
 show create table t1;
@@ -179,3 +180,44 @@ select * from t1;
 ts
 2001-09-09 04:46:40
 drop table t1;
+set new=1;
+create table t1 (a char(2), t timestamp);
+insert into t1 values ('a', '2004-01-01 00:00:00'), ('a', '2004-01-01 01:00:00'),
+('b', '2004-02-01 00:00:00');
+select max(t) from t1 group by a;
+max(t)
+2004-01-01 01:00:00
+2004-02-01 00:00:00
+drop table t1;
+create table t1 (ts1 timestamp);
+show create table t1;
+Table	Create Table
+t1	CREATE TABLE `t1` (
+  `ts1` timestamp(19) NOT NULL
+) TYPE=MyISAM
+alter table t1 add ts2 timestamp;
+set new=0;
+show create table t1;
+Table	Create Table
+t1	CREATE TABLE `t1` (
+  `ts1` timestamp(19) NOT NULL,
+  `ts2` timestamp(19) NOT NULL default '0000-00-00 00:00:00'
+) TYPE=MyISAM
+drop table t1;
+create table t1 (ts1 timestamp);
+insert into t1 values ('2004-01-01 00:00:00'), ('2004-01-01 01:00:00');
+select * from t1;
+ts1
+20040101000000
+20040101010000
+set new=1;
+select * from t1;
+ts1
+2004-01-01 00:00:00
+2004-01-01 01:00:00
+set new=0;
+select * from t1;
+ts1
+20040101000000
+20040101010000
+drop table t1;
diff --git a/mysql-test/t/type_timestamp.test b/mysql-test/t/type_timestamp.test
index 92bd20e846e..464ee63c137 100644
--- a/mysql-test/t/type_timestamp.test
+++ b/mysql-test/t/type_timestamp.test
@@ -71,6 +71,7 @@ select * from t1;
 set new=1;
 select * from t1;
 drop table t1;
+set new=0;
 
 #
 # Bug #1885, bug #2539. 
@@ -116,3 +117,34 @@ set TIMESTAMP=1000000000;
 insert into t1 values ();
 select * from t1;
 drop table t1;
+
+#
+# Test for bug #4131, TIMESTAMP columns missing minutes and seconds when
+# using GROUP BY in @@new=1 mode.
+#
+set new=1;
+create table t1 (a char(2), t timestamp);
+insert into t1 values ('a', '2004-01-01 00:00:00'), ('a', '2004-01-01 01:00:00'),
+                      ('b', '2004-02-01 00:00:00');
+select max(t) from t1 group by a;
+drop table t1;
+
+#
+# More --new mode tests
+# Both columns created before and during alter should have same length.
+#
+create table t1 (ts1 timestamp);
+show create table t1;
+alter table t1 add ts2 timestamp;
+set new=0;
+show create table t1;
+drop table t1;
+# Selecting from table in --new mode should not affect further selects.
+create table t1 (ts1 timestamp);
+insert into t1 values ('2004-01-01 00:00:00'), ('2004-01-01 01:00:00');
+select * from t1;
+set new=1;
+select * from t1;
+set new=0;
+select * from t1;
+drop table t1;
diff --git a/sql/field.cc b/sql/field.cc
index 394d53238c2..69ee6606be4 100644
--- a/sql/field.cc
+++ b/sql/field.cc
@@ -2467,8 +2467,7 @@ void Field_double::sql_type(String &res) const
 
 enum Item_result Field_timestamp::result_type() const
 {
- return (!current_thd->variables.new_mode &&
-	 (field_length == 8 || field_length == 14) ? INT_RESULT :
+ return ((field_length == 8 || field_length == 14) ? INT_RESULT :
 	 STRING_RESULT);
 }
 
@@ -2480,6 +2479,9 @@ Field_timestamp::Field_timestamp(char *ptr_arg, uint32 len_arg,
     :Field_num(ptr_arg, len_arg, (uchar*) 0,0,
 	       unireg_check_arg, field_name_arg, table_arg,
 	       0, 1, 1)
+#if MYSQL_VERSION_ID < 40100
+    , orig_field_length(len_arg)
+#endif
 {
   if (table && !table->timestamp_field)
   {
@@ -2697,7 +2699,7 @@ String *Field_timestamp::val_str(String *val_buffer,
   time_t time_arg;
   struct tm *l_time;
   struct tm tm_tmp;
-  my_bool new_format= (current_thd->variables.new_mode) || field_length == 19,
+  my_bool new_format= field_length == 19,
           full_year=(field_length == 8 || field_length == 14 || new_format);
   int real_field_length= new_format ? 19 : field_length;
 
@@ -2859,22 +2861,6 @@ void Field_timestamp::set_time()
     longstore(ptr,tmp);
 }
 
-/*
- This is an exact copy of Field_num except that 'length' is depending
- on --new mode
-*/
-
-void Field_timestamp::make_field(Send_field *field)
-{
-  field->table_name=table_name;
-  field->col_name=field_name;
-  /* If --new, then we are using "YYYY-MM-DD HH:MM:SS" format */
-  field->length= current_thd->variables.new_mode ? 19 : field_length;
-  field->type=type();
-  field->flags=table->maybe_null ? (flags & ~NOT_NULL_FLAG) : flags;
-  field->decimals=dec;
-}
-
 
 /****************************************************************************
 ** time type
diff --git a/sql/field.h b/sql/field.h
index d25ce8d4774..c42f5f63f0c 100644
--- a/sql/field.h
+++ b/sql/field.h
@@ -546,6 +546,13 @@ public:
 
 
 class Field_timestamp :public Field_num {
+#if MYSQL_VERSION_ID < 40100
+  /*
+    We save the original field length here because field_length is
+    changed to a mock value in case when the 'new_mode' is in effect.
+  */
+  uint32 orig_field_length;
+#endif
 public:
   Field_timestamp(char *ptr_arg, uint32 len_arg,
 		  enum utype unireg_check_arg, const char *field_name_arg,
@@ -587,7 +594,11 @@ public:
   void fill_and_store(char *from,uint len);
   bool get_date(TIME *ltime,bool fuzzydate);
   bool get_time(TIME *ltime);
-  void make_field(Send_field *field);
+
+#if MYSQL_VERSION_ID < 40100
+  friend TABLE *open_table(THD *thd,const char *db,const char *table_name,
+                           const char *alias,bool *refresh);
+#endif
 };
 
 
diff --git a/sql/sql_base.cc b/sql/sql_base.cc
index 8fd7273fd78..c9d6ca87fdb 100644
--- a/sql/sql_base.cc
+++ b/sql/sql_base.cc
@@ -941,6 +941,31 @@ TABLE *open_table(THD *thd,const char *db,const char *table_name,
     for (uint i=0 ; i < table->fields ; i++)
       table->field[i]->table_name=table->table_name;
   }
+#if MYSQL_VERSION_ID < 40100
+  /*
+    If per-connection "new" variable (represented by variables.new_mode)
+    is set then we should pretend that the length of TIMESTAMP field is 19.
+    The cheapest (from perfomance viewpoint) way to achieve that is to set
+    field_length of all Field_timestamp objects in a table after opening
+    it (to 19 if new_mode is true or to original field length otherwise).
+    We save value of new_mode variable in TABLE::timestamp_mode to
+    not perform this setup if new_mode value is the same between sequential
+    table opens.
+  */
+  my_bool new_mode= thd->variables.new_mode;
+  if (table->timestamp_mode != new_mode)
+  {
+    for (uint i=0 ; i < table->fields ; i++)
+    {
+      Field *field= table->field[i];
+
+      if (field->type() == FIELD_TYPE_TIMESTAMP)
+        field->field_length= new_mode ? 19 :
+                             ((Field_timestamp *)(field))->orig_field_length;
+    }
+    table->timestamp_mode= new_mode;
+  }
+#endif
   /* These variables are also set in reopen_table() */
   table->tablenr=thd->current_tablenr++;
   table->used_fields=0;
diff --git a/sql/sql_parse.cc b/sql/sql_parse.cc
index 14fc748c288..4f1a0589db1 100644
--- a/sql/sql_parse.cc
+++ b/sql/sql_parse.cc
@@ -3229,7 +3229,18 @@ bool add_field_to_list(char *field_name, enum_field_types type,
     }
     break;
   case FIELD_TYPE_TIMESTAMP:
+#if MYSQL_VERSION_ID < 40100
+    /*
+      When in in --new mode, we should create TIMESTAMP(19) fields by default;
+      otherwise we will have problems with ALTER TABLE changing lengths of
+      existing TIMESTAMP fields to 19 and adding new fields with length 14.
+    */
+    if (thd->variables.new_mode)
+      new_field->length= 19;
+    else if (!length)
+#else
     if (!length)
+#endif
       new_field->length= 14;			// Full date YYYYMMDDHHMMSS
     else if (new_field->length != 19)
     {
diff --git a/sql/table.h b/sql/table.h
index f3b0e148cc0..84df7ba127e 100644
--- a/sql/table.h
+++ b/sql/table.h
@@ -106,6 +106,14 @@ struct st_table {
 	*found_next_number_field,	/* Set on open */
         *rowid_field;
   Field_timestamp *timestamp_field;
+#if MYSQL_VERSION_ID < 40100
+  /*
+    Indicates whenever we have to set field_length members of all TIMESTAMP
+    fields to 19 (to honour 'new_mode' variable) or to original
+    field_length values.
+  */
+  my_bool timestamp_mode;
+#endif
   my_string comment;			/* Comment about table */
   REGINFO reginfo;			/* field connections */
   MEM_ROOT mem_root;