Issue with linedef type 506

I was wondering if there was a way to keep front side texture offsets when using linedef 506 (back side texture offset scrolling). At the current time it just throws them out the window and ignores any previously existing offsets for the front side of the linedef, which can be pretty annoying when trying using wide textures with scrolling.

...it doesn't throw them out, at least from my experience. Could you provide a test .WAD?

Sure thing, here ya go. I could be wrong with it throwing them out but while the textures tile properly in the editor, they certainly don't when loaded up in game.