diff --git a/src/event-mapper.ts b/src/event-mapper.ts
index 9b9384860..73d442039 100644
--- a/src/event-mapper.ts
+++ b/src/event-mapper.ts
@@ -29,7 +29,21 @@ export function eventMapperFor(client: MatrixClient, options: MapperOpts): Event
     const decrypt = options.decrypt !== false;
 
     function mapper(plainOldJsObject: Partial<IEvent>) {
-        const event = new MatrixEvent(plainOldJsObject);
+        const room = client.getRoom(plainOldJsObject.room_id);
+        let event: MatrixEvent;
+
+        // If the event is already known to the room, let's re-use the model
+        // rather than creating a duplicate
+        if (room) {
+            event = room.findEventById(plainOldJsObject.event_id);
+        }
+
+        // If no event is found or if the event found was only local we can
+        // safely create a new model
+        if (!event || event.status) {
+            event = new MatrixEvent(plainOldJsObject);
+        }
+
         if (event.isEncrypted()) {
             if (!preventReEmit) {
                 client.reEmitter.reEmit(event, [
diff --git a/src/models/event.ts b/src/models/event.ts
index f95f3f3e2..147758056 100644
--- a/src/models/event.ts
+++ b/src/models/event.ts
@@ -277,7 +277,7 @@ export class MatrixEvent extends EventEmitter {
      * it to us and the time we're now constructing this event, but that's better
      * than assuming the local clock is in sync with the origin HS's clock.
      */
-    public readonly localTimestamp: number;
+    public localTimestamp: number;
 
     // XXX: these should be read-only
     public sender: RoomMember = null;
@@ -342,7 +342,7 @@ export class MatrixEvent extends EventEmitter {
         });
 
         this.txnId = event.txn_id || null;
-        this.localTimestamp = Date.now() - this.getAge();
+        this.localTimestamp = Date.now() - (this.getAge() ?? 0);
         this.reEmitter = new ReEmitter(this);
     }
 
@@ -584,9 +584,10 @@ export class MatrixEvent extends EventEmitter {
      * Get the age of this event. This represents the age of the event when the
      * event arrived at the device, and not the age of the event when this
      * function was called.
-     * @return {Number} The age of this event in milliseconds.
+     * Can only be returned once the server has echo'ed back
+     * @return {Number|undefined} The age of this event in milliseconds.
      */
-    public getAge(): number {
+    public getAge(): number | undefined {
         return this.getUnsigned().age || this.event.age; // v2 / v1
     }
 
@@ -1269,6 +1270,8 @@ export class MatrixEvent extends EventEmitter {
             // emit the event if it changed
             this.emit("Event.localEventIdReplaced", this);
         }
+
+        this.localTimestamp = Date.now() - this.getAge();
     }
 
     /**
diff --git a/src/models/thread.ts b/src/models/thread.ts
index b882f7904..85f94b986 100644
--- a/src/models/thread.ts
+++ b/src/models/thread.ts
@@ -77,8 +77,6 @@ export class Thread extends TypedEventEmitter<ThreadEvent> {
         });
         this.reEmitter = new ReEmitter(this);
 
-        this.initialiseThread(this.rootEvent);
-
         this.reEmitter.reEmit(this.timelineSet, [
             "Room.timeline",
             "Room.timelineReset",
@@ -92,6 +90,7 @@ export class Thread extends TypedEventEmitter<ThreadEvent> {
         } else {
             this.id = rootEvent.getId();
         }
+        this.initialiseThread(this.rootEvent);
 
         opts?.initialEvents?.forEach(event => this.addEvent(event));