Yeah, I can imagine the following scenario:
Open editor on topic A, accidentally type in something
Collapse editor, maybe forget about it
Go to another topic, B
Expand editor and start typing a reply to B
During the course of research for the reply to B, go to your user page or any other non-topic page
Click submit, notice that the dialog is not for A
Contrived coincidence, but still. It's also just another Enter press instead of an Ok/Cancel dialog. Ctrl-EnterEnter
Now that I think about it, I think I've hit that exact key sequence from my profile page to confirm a reply.