I have just spent my day fighting Snarby [who is awesome] a handful of times to get my shield, however when I use the shield for the first time against an Alpha Voltail [Depth 2 of the Snarby gate] it breaks immediately, and then I take damage - both piercing and normal, by the colours. Nearly killed me, the nasty little thing.
My gear was all level 2 [heat] Wolver stuff with a Beast Basher, if that's relevant.
It appears as though all other damage is mitigated normally. Perhaps it was simply the single Voltail which has the ability to break it in one hit?