Cracks in polygons in BSP Optimize

This problem also occurs when the Create Convex Polygons checkbox is checked in the Pen tool.

1. Create a 5-sided cylinder in BSP
2. Go into "Brush Editing" mode
3. Select the top face and click on the "Optimize" tool

Result: the top face is now split into two faces, and they have a small gap between them due to one vertex being slightly offset from the other one.