It's no rare occurence for PvP to extend across transitions. This is fine. What isn't fine is when these transitions are abused. "Prairie dogging," when somebody crosses a transition only to step back through it right after attacking/being attacked, is very much against our rules.
One area in particular, the In-Between, is especially plagued by this sort of transition abuse. You cannot climb several hundred steps and continue as if nothing happened. This is mostly a problem with Upper friendly characters scaling the staircase down into Lower Sanctuary to attack for a short while, then climb up again and almost immediately find safety on the other side of the gates.
If you're going to use guerilla tactics, don't use the engine's short comings to your advantage. We'll be taking further steps to prevent this sort of abúse, but that really should not be necessary!