Comment 5 for bug 569914

I can confirm that all that is required is a click on the menubar outside of any menu item. Emacs then appears to completely freeze (the cursor stops blinking, no text is placed in the buffer when you type, and if the mini-buffer was active, it also does not accept any text).

Clicking on any menuitem causes emacs to unfreeze (the cursor begins to blink again) and the various buffers once again accept input.