Comment 17 for bug 1362358

I've set a warkaround in guvcview for this buggy behaviour, if bytesused is zero guvcview will now use the length field.
It serves as a workaround but this clearly violates the v4l2 api:
http://linuxtv.org/downloads/v4l-dvb-apis/buffer.html

bytesused - ... Drivers must set this field when type refers to an input stream, ...

you can try my testing ppa:
https://code.launchpad.net/~pj-assis/+archive/ubuntu/testing/+packages

build is pending, but it should be available in an hour or so.