diff --git a/manifest b/manifest
index e3cc0013f4..feaba5c150 100644
--- a/manifest
+++ b/manifest
@@ -1,5 +1,5 @@
-C Automatically\sclose\sephemeral\sb-trees\swhen\stheir\slast\scursor\sis\sclosed.
-D 2021-03-18T14:31:37.348
+C Further\ssanity\schecking\sof\sthe\sOpenDup\scursors.
+D 2021-03-18T15:42:59.646
 F .fossil-settings/empty-dirs dbb81e8fc0401ac46a1491ab34a7f2c7c0452f2f06b54ebb845d024ca8283ef1
 F .fossil-settings/ignore-glob 35175cdfcf539b2318cb04a9901442804be81cd677d8b889fcc9149c21f239ea
 F LICENSE.md df5091916dbb40e6e9686186587125e1b2ff51f022cc334e886c19a0e9982724
@@ -483,7 +483,7 @@ F src/auth.c 08954fdc4cc2da5264ba5b75cfd90b67a6fc7d1710a02ccf917c38eadec77853
 F src/backup.c 3014889fa06e20e6adfa0d07b60097eec1f6e5b06671625f476a714d2356513d
 F src/bitvec.c 17ea48eff8ba979f1f5b04cc484c7bb2be632f33
 F src/btmutex.c 8acc2f464ee76324bf13310df5692a262b801808984c1b79defb2503bbafadb6
-F src/btree.c b048dcb502fd8abd5b161189150607d8ca9477b52fc5cba907246f795eb1fe36
+F src/btree.c 25cdff8bd4b3c9bb009bfe585a7edde48fdb9aa1579173922038aac6bb47c0c6
 F src/btree.h 096cc53baa58be22b02c896d1cf933c38cfc6d65f9253c1367ece8cc88a24de5
 F src/btreeInt.h 7614cae30f95b6aed0c7cac7718276a55cfe2c77058cbfd8bef5b75329757331
 F src/build.c fec73c39d756f31d35ccbaa80fe1e040a8d675a318d4d30f41c444167bf3b860
@@ -614,9 +614,9 @@ F src/upsert.c df8f1727d62b5987c4fd302cd4d7c0c84ae57cd65683c5a34a740dfe24039235
 F src/utf.c ee39565f0843775cc2c81135751ddd93eceb91a673ea2c57f61c76f288b041a0
 F src/util.c 41c7a72da1df47864faa378a1c720b38adb288c6838cb6be5594511b6287a048
 F src/vacuum.c 492422c1463c076473bae1858799c7a0a5fe87a133d1223239447c422cd26286
-F src/vdbe.c 819860625f65ebc1ad029fbef07b62c56904e057a6d76f0d5486e2c41d0fccd4
+F src/vdbe.c cba3e495c8ab25af825202dfa944e6f91d5c5cf86d415af07cac3834989d64a6
 F src/vdbe.h 25dabb25c7e157b84e59260cfb5b466c3ac103ede9f36f4db371332c47601abe
-F src/vdbeInt.h 3df118924e1711f1bbc8e30c46260d0ab6c3b029b32dd411f789111f76434f3c
+F src/vdbeInt.h 000d9ab1ea4cb55a80de15e28f3f595645b4fddef34bca4347fb3db8031d9041
 F src/vdbeapi.c 4a43e303ec3354c785f453e881521969378e85628278ab74ba4a9df790c0d93b
 F src/vdbeaux.c 6df834c4ff0c86a62b94fe0762d0abb7dbda54a862f0fe82e35d22fc4490414d
 F src/vdbeblob.c 253ed82894924c362a7fa3079551d3554cd1cdace39aa833da77d3bc67e7c1b1
@@ -1910,7 +1910,7 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
 F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
 F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
 F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
-P b8de980b2fb78088ef74e053cb987bb84319d13dc96ce1e89baaaa3fe8cf1efc
-R d059e62ed2003127849996336a75bcfd
-U dan
-Z 5c6f726925b0e9cfdd8d4a838991a1a4
+P 39b5af18c0580c8e92516d410f8c465bfec31b2d0be9df1cfd6a1d1a19b4fc14
+R a76f75bf1ec726e3bc7a2a3639bd46d6
+U drh
+Z 8ca7de05c1a42b71a557e12a74405656
diff --git a/manifest.uuid b/manifest.uuid
index 556c036b9c..aa2b3946c6 100644
--- a/manifest.uuid
+++ b/manifest.uuid
@@ -1 +1 @@
-39b5af18c0580c8e92516d410f8c465bfec31b2d0be9df1cfd6a1d1a19b4fc14
\ No newline at end of file
+0ec71cf16983697f68ab8d921d80a5f39611e4cb5e6e19cbc4a9ad6d49bfc835
\ No newline at end of file
diff --git a/src/btree.c b/src/btree.c
index 830e3555a9..d7dddde1a5 100644
--- a/src/btree.c
+++ b/src/btree.c
@@ -2737,20 +2737,24 @@ static void freeTempSpace(BtShared *pBt){
 */
 int sqlite3BtreeClose(Btree *p){
   BtShared *pBt = p->pBt;
-  BtCursor *pCur;
 
   /* Close all cursors opened via this handle.  */
   assert( sqlite3_mutex_held(p->db->mutex) );
   sqlite3BtreeEnter(p);
-  pBt->openFlags &= ~BTREE_SINGLE;
-  pCur = pBt->pCursor;
-  while( pCur ){
-    BtCursor *pTmp = pCur;
-    pCur = pCur->pNext;
-    if( pTmp->pBtree==p ){
-      sqlite3BtreeCloseCursor(pTmp);
+
+  /* Verify that no other cursors have this Btree open */
+#ifdef SQLITE_DEBUG
+  {
+    BtCursor *pCur = pBt->pCursor;
+    while( pCur ){
+      BtCursor *pTmp = pCur;
+      pCur = pCur->pNext;
+      assert( pTmp->pBtree!=p );
+
     }
   }
+#endif
+  pBt->openFlags &= ~BTREE_SINGLE;
 
   /* Rollback any active transaction and free the handle structure.
   ** The call to sqlite3BtreeRollback() drops any table-locks held by
diff --git a/src/vdbe.c b/src/vdbe.c
index a6bfd236cd..73ff2d6270 100644
--- a/src/vdbe.c
+++ b/src/vdbe.c
@@ -272,11 +272,6 @@ static VdbeCursor *allocateCursor(
 
   assert( iCur>=0 && iCur<p->nCursor );
   if( p->apCsr[iCur] ){ /*OPTIMIZATION-IF-FALSE*/
-    /* Before calling sqlite3VdbeFreeCursor(), ensure the isEphemeral flag
-    ** is clear. Otherwise, if this is an ephemeral cursor created by 
-    ** OP_OpenDup, the cursor will not be closed and will still be part
-    ** of a BtShared.pCursor list.  */
-    if( p->apCsr[iCur]->pBtx==0 ) p->apCsr[iCur]->isEphemeral = 0;
     sqlite3VdbeFreeCursor(p, p->apCsr[iCur]);
     p->apCsr[iCur] = 0;
   }
@@ -3873,7 +3868,7 @@ case OP_OpenDup: {
 
   pOrig = p->apCsr[pOp->p2];
   assert( pOrig );
-  assert( pOrig->pBtx );  /* Only ephemeral cursors can be duplicated */
+  assert( pOrig->isEphemeral );  /* Only ephemeral cursors can be duplicated */
 
   pCx = allocateCursor(p, pOp->p1, pOrig->nField, -1, CURTYPE_BTREE);
   if( pCx==0 ) goto no_mem;
@@ -3884,6 +3879,8 @@ case OP_OpenDup: {
   pCx->pgnoRoot = pOrig->pgnoRoot;
   pCx->isOrdered = pOrig->isOrdered;
   pCx->pBtx = pOrig->pBtx;
+  pCx->hasBeenDuped = 1;
+  pOrig->hasBeenDuped = 1;
   rc = sqlite3BtreeCursor(pCx->pBtx, pCx->pgnoRoot, BTREE_WRCSR, 
                           pCx->pKeyInfo, pCx->uc.pCursor);
   /* The sqlite3BtreeCursor() routine can only fail for the first cursor
@@ -3950,9 +3947,10 @@ case OP_OpenEphemeral: {
     aMem[pOp->p3].z = "";
   }
   pCx = p->apCsr[pOp->p1];
-  if( pCx && ALWAYS(pCx->pBtx) ){
-    /* If the ephermeral table is already open, erase all existing content
-    ** so that the table is empty again, rather than creating a new table. */
+  if( pCx && !pCx->hasBeenDuped ){
+    /* If the ephermeral table is already open and has no duplicates from
+    ** OP_OpenDup, then erase all existing content so that the table is
+    ** empty again, rather than creating a new table. */
     assert( pCx->isEphemeral );
     pCx->seqCount = 0;
     pCx->cacheStatus = CACHE_STALE;
diff --git a/src/vdbeInt.h b/src/vdbeInt.h
index 4f8a2edf37..cb423f20a1 100644
--- a/src/vdbeInt.h
+++ b/src/vdbeInt.h
@@ -86,6 +86,7 @@ struct VdbeCursor {
   Bool isEphemeral:1;     /* True for an ephemeral table */
   Bool useRandomRowid:1;  /* Generate new record numbers semi-randomly */
   Bool isOrdered:1;       /* True if the table is not BTREE_UNORDERED */
+  Bool hasBeenDuped:1;    /* This cursor was source or target of OP_OpenDup */
   u16 seekHit;            /* See the OP_SeekHit and OP_IfNoHope opcodes */
   Btree *pBtx;            /* Separate file holding temporary table */
   i64 seqCount;           /* Sequence counter */