I've noticed a spot in the gnoll quest where you enter a door and are immediately in the middle of a small group of gnolls. I think that this is... an exploit that works against the PCs, instead of the other way around.
Realistically, you would hear them or open the door and peek down to see them. Running in straight away would be stupid and, for most people, out of character... but that's what you're forced to do in this case.
I do like the challenge of it, but it would be a lot nicer if it were more legitimate. For example, a location message saying:
*armed gnolls leap from a short cliff above you!*
or something like that.
Another option would be to make the transition somewhere further back... like extending the hallway leading to the door with a transition point.
Once, I had a party that was doing some... very sketchy/meta-ish stuff. This doesn't help the situation either because it limits how far you can run or hide from spells, the "you-know-whats", etc. and also provides a free escape route, as I have never seen a gnoll chase a group up the ramp and through the transition.
What do ya think?