Its because you have both barrier and teleporter on the same tile. Due to the technical implementation of pathfinding (which was not designed for teleporters and got a bit tweaked) and performance considerations, it assumes this path is valid. Gameplay-wise it must not make much difference since it changes a path only for a half of tile. Since usage of both teleporter and barrier on neighboring tiles is highly unlikely in attempt to make any major difference in map's strategy and considering performance impact this fix may cause, I'll just say I'll not fix that but thanks for pointing out!