Combined QML-C++ debugging not working on windows

Enabling both QML and C++ debuggers in the Project debugger settings doesn't work - in the application output I get:
Debugging starts
Qml debugging is enabled. Only use this in a safe environment!
QDeclarativeDebugServer: Waiting for connection on port 3768...

but no connection. If I disable C++ debugger everything works and I get:
Debugging starts
Starting D:\Qt\dev\qmltest-build-desktop\debug\qmltest.exe "-qmljsdebugger=port:3768"
QDeclarativeDebugServer: Waiting for connection on port 3768...
QDeclarativeDebugServer: Connection established

The test app is launched in both cases. For reference, with the same Creator and Qt versions combined QML-C++ debugging does work for Symbian (although with one minor patch from me in the symbian-specific bits that's not yet in master)

Debugger log for working QML only and non-working QML&C++ cases attached.