This is only reproducible when using the Basic qt quick controls style.

Steps to reproduce:
Run the dialogs manual test with the Basic style.

qtdeclarative/tests/manual/quickdialogs/dialogs

Turn on "ShowAlphaChannel", then open the ColorDialog.

Click on the ComboBox that says "Hex", then select "RGB". (resizing the window might be necessary)
Click on the ComboBox again, and click "HSV".
Click on the ComboBox again, and click "RGB"
Click on the ComboBox again, and click "HSV".
Click on the ComboBox again, and click "RGB"
Click on the ComboBox again, and click "HSV".

The last click causes the application to crash.