No video received if eth unplugged

[JanMatas]

I have encountered a strange issue with this module. It works flawlessly when ethernet cable is plugged in to pi, but whenever I start reading when ethernet is unplugged, the driver fails to provide video (any program - opencv code, cheese, camorama stalls with black screen and there is this error:

VIDIOC_DQBUF: No such device.

Any ideas?