First off, thanks for developing and maintaining an awesome mail client! This bug has been around for some time... Steps to reproduce: 1. Open a compose window 2. select the message content text-box and type some text 3. select the subject text-box and then type some text 4. press control-z to undo Result: message content text-box text is removed Expected: subject text-box text is removed. Undo should undo the last action in the selected text-box, or across the entire compose window. It shouldn't only affect the message context text-box.
*** Bug 4236 has been marked as a duplicate of this bug. ***