[BUG] r_letterbox affects warpzones?

Here's some pictures of a warpzone with and without r_letterbox enabled:

Without:


With:


If you look closely at the 'with' picture you'll see a faint black line where the warpzone is. In the game the warpzone behaves as if the entrance is out of alignment with the exit by a small amount.

Is this a bug or just a problem at my end?

This definitely looks like a bug.