To reproduce this bug:

1. Open the view "Ultrasound Support"
2. Create a new video device, Webcam as dummy image is fine
3. Activate Device (you should see the live image, possibly global reinit is requried)
4. Switch to tab "US imaging"
5. Click "Freeze"
6. Click "Freeze" again to unfreeze => nothing happens, the application freezes, somtimes it reacts after a few seconds, sometimes it crashes