First of all, I don't think polearm spec mobs can ever succeed with entrap. They just do the "initial" part of the skill, but the second part that involves the actual disarming never happens. I'm not sure but it *may* have been like that before the weapon slot change though.

Another one: crescent kick. I haven't seen it disarm in ages, at least since the weapon slot change; maybe it's checking the wrong slot?