Lately I've been trying to create a forest in Bryce and I keep getting what looks like broken polygons on any tree that is too near or too close (from a perspective point of view) to another tree. I've included a picture that is not an example of the forest I'm trying to make, but an example of the problem. Notice the second, fourth and sixth tree from the left. They seem to have polygons missing. Am I missing something here or is there a bug? I tried re-installing and even installed the update and it's no good...

Any advice about this phenomenon would be great...