I'm not sure at which version this changed, but I have long been used to being able to edit a pending message (queued via "Send Later") by using "Edit Message" on a box in the outbox.  Once I had finished editing the message, I used "Send Later" to save it.  The result was that the message in the outbox was edited in place.  Now when the edited message is saved via "Send Later", this queues the edited copy of the message as a new message in the outbox alongside of the original message.  This is quite astonishing compared to previous behavior, especially since the primary reason I use "Send Later" is that I can edit pending messages before finally sending them.

Reproducible: Always

Steps to Reproduce:
1. Compose a message and use "Send Later" to save it in outbox.
2. Use "Edit Message" (e.g. via 't') to edit the message in the outbox and save it via "Send Later"
3. Check the outbox and find both copies of the message (original and edited)

Actual Results:  
Both copies of the message in the outbox.

Expected Results:  
Only the edited copy of the message in the outbox.