Fixed Linedef Type 07 affects the sky rendering

Download the same wad I posted in this topic:

http://mb.srb2.org/showthread.php?t=35537

Test it on Software rendering.

Once loaded, walk, turn your view around and keep looking at the sky. You'll see the sky will "pops" or "jumps" at bit.

Remove the Linedef Type 07 from the map, and the bug ceases.

EDIT:

Fixed the topic tittle.

The sky offset seems to change the moment aligned flats appear onto the screen.