This sometimes happens when you save your drafts on an IMAP server. Maybe you can change your configuration to store the drafts locally? Go to Tools -> Account Settings -> [account] -> Copies & Folders -> Drafts & Templates and choose to Keep messages drafts in Drafts folder on Local Folders...

Thank you! It was close... When I did exactly as you described, it put them into the Local Folders at the very bottom (I have a lot of folders in between), rather than the normal Drafts folder near the top. However, your tip led me to the right place... Here's what I did that worked:

Tools>Account Settings>[account]> Copies & Folders> Drafts & Templates and then chose to Keep Messages Drafts in "Other" and then selected [account]>"Drafts". Now they appear in the normal Drafts folder, just once, and it is properly deleted when I hit "Send".

Thank you so much, Onno Ekker !!

@flyingpianos Thanks for your workaround....! This has been aggravating me so much since the last three updates (31.2 , 31.3, and 31.4). But that's what it is, a workaround, and does not address that these updates have broken this part of Thunderbird, and needs to be fixed.

Has this been entered as a bug with the Mozilla team...? It needs to be.

Having to manually go into the Thunderbird/Tool/Account Settings/account/Copies & Folders/Drafts & Templates Options area and telling it to save drafts in the drafts folder instead of the drafts folder which is the default, is ridiculous, and simply shows that the autosave feature has been broken with these releases and needs to be addressed by the developers.

How do we bring this to the attention of the Bugfix Team at Mozilla, and get this defect actually addresssed and fixed properly...? I don't see anywhere to report or post bugs to the development team.