Sure enough.  Thanks for reporting this, it's fixed on the trunk.

I've only seen the problem in Firefox on Linux, but it happens consistently from
the few machines I've tried.   Clicking the select pops up the options as
expected, but moving the mouse pops the options back down so they can't be
selected with the mouse (selection with the keyboard still works).   
Seems to be due to nesting the select inside a list item.  Converting the ul and
li tags to divs fixes the problem.
Problem can be reproduced on the demo site (http://deformdemo.repoze.org/select/).