I fought a bunch of them in T3, both in clockworks and arenas. They kept teleporting outside the borders, and I had to wait for them to willingly come back inside, while menders healed them back to full.
They can also teleport to the "safe side" of a force field.
They can also teleport into bushes.
http://img515.imageshack.us/img515/9868/spiral20120202055222.png