Long hang when selecting item

Steps to reproduce:

• Install QDS 3.3 via the online installer
• Start QDS 3.3
• Disregard the welcome nag screen
• File => New File
• Qt Quick Controls => Custom Button
• Select path/name ( mine is: /Users/mtillmanns/projects/qt/design-stuff/btn-test/MyButton.ui.qml )
• Click inside the checkerbox'ed area

Afterwards the app hangs for 2-5 minutes ( see qds33sample.txt for a sample of the callstack ).

Once the hang is done, clicking outside the checkerbox'ed area once, then click inside it again, repeats the hang.