Only thing I've seen remove the defensive stances, buffs etc is the bard dispel. I've never managed to remove it with pushing hands.
To perform decent xp in certain areas you simply need to have a bard to dispel all the "short duration small mitigation buffs" of 50%+ that are way overdone both in potency and rarity (well, lack of rarity).

Dosen't work on the "bubble" defensive stance either though - which is the first encountered.
Oh, but that's a buff aswell, as mobs are not using stances. The only real use would be against other players, and there it (chockingly enough) does nothing either. ;p

Nod nod, but they aren't "stances" as for players, rather just a buff which includes the name Stance in it - they do wear off - coincidently wearing off and landing a pushing hands in the same area is what made me in the beginning think I could actually push mobs out. However, I've never ever succeeded on doing it within the first 30ish seconds (even with a chance of failure, it should actually succeed early at some point), which leads me to believe that the buff simply wears off.

It does for me, although I do not know how it reacts with stances that either decrease or increase the END cost of abilities.