Steps to reproduce:

• use a qtbase developer build
• open any application and deploy to an iOS simulator (e.g. the menus example)
• set a breakpoint for debugging
• start debugging the application in the simulator device
• stop the debugger (Debug->Stop Debugger / hit red square)
• start debugging the application again

=> The simulator device will be black, Qt Creator's debugger will fail to deploy.

Workaround:
Close the simulator manually, after having stopped the debugger.

Additional information:
XCode manages to re-use the simulator after the debugger was stopped.