SX30 is filter adaptor - needed or not?

I'm new around here, and mostly interested in discussing my Nikon D3100, but I have a question regarding my girlfriend's SX30 is superzoom. So hi.

She has had two 52mm Kenko UV filters break whilst on the camera, when it was in its bag, in her rucksack, whilst riding her motor scooter. The lens cap stayed on both times. She hasn't (consciously) mistreated it, but obviously something isn't right.

The salesman in the shop sold her the filter as a lens protector, and I think that's sensible, but obviously something isn't right.

Without getting into the discussion of the probable poor optics of this cheap filter, why might they be breaking so easily? I'm leaning towards one of:

1) Crappy filter.

2) Not using a filter adaptor for this camera. I read that it should not have filters screwed in directly, but then some people have reported success from what I have read.
3) Crappy bag (don't remember who the manufacturer is).

All advice appreciated, we are a bit confused.