Casting sight on marked low slabs causes graphical glitches

[Loobinex]

To reproduce:

1. Add to the original campaign first level this script: MAGIC_AVAILABLE(PLAYER0,POWER_SIGHT,1,1)
2. Cast Sight east of the gold to see water
3. Mark the water slabs so you remember where they are -> When Sight is finished, notice it now looks weird:

In the original game and the keeperfx 0.4.8 release this was not the case

[Loobinex]

The bug is bigger:

1. Mark an unexplored slab for digging where you know is path, lava, water or any other low slab
2. Cast sight of evil on it
3. When sight of evil is done, the slab is concealed again, but the marking is now glitched.