The Gate Key which is obtained from a certain NPC in a certain Lowerdark Quest, needed to open the gate towards the boss, is not removed from an inventory after a server reset.
The Gate does not automatically lock itself again either.
Sorry, I don't know the Quest's name from the top of my head but I imagine it will not be hard to find.
Despite this being a terribly non-specific bug report I was eventually able to figure this out and fixed it.
Glad I could set an example :$