Comment 12 for bug 459586

A little update:

After having this problem again I started some tinkering:

sudo rmmod uvcvideo gspca_ov519 gspca_main vloopback videodev V4l1_compat
sudo modprobe videodev gspca_ov519 vloopback v4l1_compat uvcvideo

Now the webcam works :-)