i'm not fully sure this is a bug, although to me it certainly seems so.
first observed while fighting phase spiders: charname was doing recon while rest of party stayed by the edge of the map. some phase spiders attacked charname on the far end of the map, but unespectedly teleported also beside the rest of the group. like they would have a godike knowledge on where to look....
this actualy works both ways: when i attacked devaeron my charname knew exactly where to run and attack despite the mob teleporting way out of anyone's sight. in effect charname was running room to room chasing down devaeron after his every teleport, and always to correct room
i don't recall experiencing this pre 1.2 but i can't verify.
so: CURRENT BEHAVIOR: both party members and enemies will continue attacking/chasing the adversary despite the latter vanishing out of sight. phase spiders are able to locate and attack (teleporting in the sweet spot) the party members they have no sight or knowledge on
EXPECTED BEHAVIOR: when a character (either we or enemy) goes out of sight into fog of war, neither party memeber nor an enemy should have inherent knowledge on where to chase and attack this character. phase spiders should not have knowledge on party members they had no chance to witness - thus should not be able to teleport to them and attack.