The common definition of edge orientation is that an edge is oriented correctly if, when placed in its correct position with <L,R,U,D>, it is oriented correctly. A consequence is that <L,R,U,D> can't change the orientation of an edge- it would be a horrible definition for edge orientation if the process for determining edge orientation could change edge orientation. (Heisenberg Uncertainty Principle for the cube? xD)
I don't know if that's satisfying enough for you. Ryan Heise's site has a bit of information on it. This thread (
http://www.speedsolving.com/forum/showthread.php?t=21630&highlight=proof+permutation) is a good read, also. Post 27 has some good info.
THAT'S A BINGO!
*cough*
http://www.jaapsch.net/puzzles/pgl25.htm
I found it. I should've thought to check Jaap's site immediately. That should give you what you're looking for. The thread that lead me there (
http://www.speedsolving.com/forum/showthread.php?t=17908&highlight=proof+permutation) is also good reading.