I remembered this issue when I read
Thor's post, but this error exists on v5 (have yet to try on v5.3).
If you enter a level through a level link that puts you directly on top of a level link, you can walk around on the level you entered but the server thinks you are in the level that the level who's link you were put on top of.
Example: The blob level on Maloria had two exists, both leading back to the overworld (mal.gmap). The top one placed you directly on top of a level link on the gmap leading back into the blob level, which made the client think the player was in mal.gmap letting it walk around everywhere and clientsided NPCs were responding to the player and everything. However, if you opened RC and checked what level the player was in, the server showed it as the blob level, and all the baddies inside that level kept attacking the player.
Quite severe bug I'd say. If Stefan needs to test it I can set it up online, but I fixed this issue by simply not putting the player on top of a new level link when exiting the previous level.