Seems like some changes were made to the pathing of teleport abilities since the last major patch. Some good, but then there is a change that is extremely exploitable, and guessing was unintended, in WvW.
There are certain sections of walls and keeps that allow for players with teleport abilities to port onto the top of the walls from the outside. Please examine the issue and fix it ASAP. Contact me if you would like further details.
PS.
As a side note, there is a related bugs with the walls and AI creatures/pets. Both mobs and pets seem to be able to walk through walls. This was discovered by a guildie who shot an oakheart with the cannon, where said oakheart decided to walk through the wall, up the stairs, and attack him.