Polygon collision problems

[Muxeu]

Hi ! Thx for great engine. But i have a problem.

Sometimes triangle polygons don't work properly. This problem occurs
when the triangle falls on object exactly the same length and exactly
at same position.

Image:
http://demiart.ru/forum/uploads8/post-880438-1316948255.jpg

Left triangle fall through rectangle. Right works perfectly. Bodies
has same material.

Triangle code:
return [ new Vector2D(-size_x, size_y), new Vector2D(size_x, size_y),
new Vector2D(0, -size_y) ];