Open Radar

 
This is tricky to describe, but basically, if you use OS X's built-in "Speak selected text when the key is pressed" shortcut (as set in System Preferences > Dication & Speech > Dictation) within an app, it will break apps that work with windows in that app. 

Text-to-speech doesn't have to be active for the breakage to occur, it just has to have been used - but ONLY from the built-in shortcut. If you activate it using the menus (Start Speaking and Stop Speaking), or even a keyboard shortcut to those menus, the problem does NOT occur. It always -- and ONLY -- occurs when using the built-in toggle as set in System Preferences > Dictation and Speech.

The problem is visible when you use any app, like our own Moom or Andreas Hegenberg's BetterSnapTool, that helps users manage windows. If you use these apps after invoking the shortcut from System Preferences, the window will not quickly and smoothly move and resize when requested by such apps. Instead, it jerkily moves across the screen, and doesn't properly resize, and may not even move to the proper location.

If you quit and relaunch the app in question (not Moom, but the app you invoked text-to-speech in), then Moom etc. will work fine - but only until you again invoke text-to-speech via the System Preferences toggle.