Can't speak to #2, but as for lolstab....
It's simply the thrust attack on most 2hand swords. The animation for the attack makes it very powerful. Many long reach weapons will not make effective contact at very close range, but even long 2hand swords will do full damage on a lolstab to someone immediately next to them, despite the fact that practically speaking, there should be no room to actually swing your weapon. Pre-patch it also received a reach bonus that made it just as long and effective against cavalry as most spears. I believe this aspect was reduced in the patch. I think.
Come to think of it, for #2, are you using a throwing weapon in these instances? If so, you're stumbling because any player with a ranged weapon equipped will stumble when they come into direct contact with an enemy. No damage is actually dealt, but your guard will go down so they can hit you. If this is what's going on (just assuming) then you simply need to switch to melee mode on your weapon when they get next to you.
