Hang after toolbar use - easy to reproduce

[David Reitter]

Hi,

I have this hang that a bunch of users are complaining to me about.  I’m trying 
to diagnose this, but I’m not sure where else to look.

It’s easy to reproduce (on a Mac, anyway):  Emacs -Q, then double-click any 
available icon in the toolbar.  The bug occurs for individual clicks as well, 
just not as reliably for me - but the hang is a major issue for some users, as 
it seems.  Emacs stops reacting to input or redrawing the screen.

http://debbugs.gnu.org/cgi/bugreport.cgi?bug=18848

Any pointers would be appreciated.

D