Algodoo

Looks like you used the subtract tool to get that shape. I'll bet you had two boxes in place, subtracted one, then subtracted the other. The first box you subtracted also subtracted its outline from the second box, and when you subtracted from the second box it didn't quite overlap with the area the first box removed. The result is a near-infinitely thin projection covering most of the hole along the line where the boxes originally overlapped. I'd call it unwanted behavior in the CSG, not a true glitch. It's happened to me before, and it's a pain in the butt.

What Frank said.

No need to use CSG - U can draw very thin line from console with scene.addbox command...

i think if it isnt csg or wat kilinich said, its obviously a polygon that was drawn in such a way that it created a small line that you cant really see, like maybe say, by not closing the polygons edges before finishing it, or your mouse fell off the table... or... something...

lololololz

ya its just a very thin line use the cut tool