It actually appears that the Developer Tools are moving off the active screen (and in a minimized state):
So what is actually happening:
The developer tools are opening (just not on the active screen).
In order to bring it up:
- Select 'Developer Tools' as your active window (Hotkey: Alt+Tab)
- Type Alt+Space to bring up the system menu
- Select "Move" and then re-position the Developers tools to the active screen
- Re-size the window