Running "through" walls accidentally in the battle fields, is unfortunately a known bug... Many attempts has been made to fix it completely, but alas, it still happens, although its fairly rare with the last patch... before the patch, it was a given... that somewhere you WILL end up on the wrong side of the wall...
THe quickest way to fix it when it does happen, is select the character that is NOT in the wall, and change to the main game, then come back if needed. (the same for when that happens in the main game, Select the character NOT stuck, change to the BF and come back)
Both characters will be where the selected character was last.... which is why you need to select the NON-stuck one...
P.S. Instead of changing to the BF / Main game, you can also just go up / down stairs and it will have the same effect. Un-walling your character.
<img src="/ubbthreads/images/graemlins/winkwink.gif" alt="" /> bleming walls that wants to eat us all up....
Seems like he just ran through the wall 
)