This doesn't fix the only bug I've experienced: The "Store draft messages on the server" Mailbox Behavior option is still not being properly respected or stored. It seems to be permanently on. While you can disable it temporarily, it always reverts back on. It's not a terribly big deal, but it is annoying due to the implementation of Mail's autosave - the trash folder rapidly becomes populated with hundreds of incomplete drafts as Mail.app trashes the previous save and creates a new one.

I've not tested it yet, but I would guess that this could be exceptionally bad with large attachments.