What causes holes in your models ?

[Cowboybebop]

Originally Posted by Andy Colebourne

Make a rectangle in the plan view. Select one vertex and pull it upwards in the front view. Now all points are not on the same plane. Although AC3D copes quite well with this shape, this non-planar rectangle should really be triangulated since all the points are not 'flat' on the same plane.

Andy

Ok, I get that but why doesn't it turn red ad become a hole ?