I just bumped into to unexpected things when reviewing the reopen queue.
Firstly, when clicked "Leave Closed", I got a popup asking "Nominate this question for reopening?". Thinking that perhaps I accidentally clicked Reopen rather than Leave Closed (pretty sure I didn't, though), I just closed it (did not click yes or no).
Secondly, closing the dialog (not clicking yes, not clicking no) moved onto the next item (which happened to be the "no items left" page). Going back, it appears I voted to "Leave Open".
The particular post I was reviewing was this one.
I would expect that closing the dialog would cancel whatever action was pending (reopen), rather than actually perform the action opposite of what it is suggesting (voting to leave closed). Additionally, I wouldn't expect the reopen confirmation to pop up on a "Leave Closed" vote.
(Yes, the result was what I intended, but the process was not at all correct.)