Steps:

1) Browse to a topic
2) Open the quick-mod tools and select an AJAX option (lock/delete/etc)
3) A popup will open, to confirm your choice
4) Close the popup by clicking on the "close" button (or anywhere outside the popup)
5) Put your cursor in an input form like "search this topic", or quickreply
6) Hit return/enter

In fact, you don't even need to try to fill in a form (although this is a likely scenario). Hitting return in general will still trigger the AJAX request.

I haven't had time yet to properly investigate. But I'm assuming we should unbind the keys on popup close.