[Therion] bug encounter

Hello, I have a bug in my (old) release of therion (5.2.8) It's on the drawing of the area (swump area) witch represent a house over a cave. We have a triangle white, I think the software have a problem to calculate the correct surface. I try to split the line (one only line for all the cave), nothing change. It's not a probleme for me. I give it to you to reproduce the bug if it's useful. On the plan, I put the cave uper the house, it's normal, it's to see the cave. Thanks a lot for your work. Gilbert