This was more a problem in the demo than the release version, and I think much more in the battlefields than the main game. I'm not sure if any of the patches have addressed this, however.
If you have one character in the normal play area, going through an entrance/exit will teleport the other character there. You may be able to toss a teleporter into the play area, or if one character is still there, simply drop one and teleport a shot distance to it. In the demo sleeping in a haystack would teleport the out of bounds character to the other one, but I have not run into this problem in the release version, so have not tried that fix. You can stand beside a wall, and then enter and leave the BF to try to get to the other side. In the BF dungeons, you can simply exit the battlefield and re-enter it.