Unexpected result for OCCGeometry shape subtraction


I have created a 3D spiral using OCCGeometry in much the same way as threads are created in the OCC bottle tutorial. The spiral itself looks fine when I visualize it. However, when I try to cut the spiral using shape subtraction (e.g. to make its edge serrated), I do not get the expected behaviour. Sometimes, I get a different shape than expected, but, most of the time, I get no shape at all. This happens even when visualizing the compound of the shapes used in the subtraction show that they have a non-empty intersection.

The simplest code I have been able to write that reproduces the problem can be found in this gist:

The first call to GeoDraw in this code produces an empty stage only.
The second call visualizes both the spiral and the box successfully.

The gist also includes my attempt at making a simpler example demonstrating the problem, where I cut a cylinder instead of a spiral. However, the cutting works just fine in that case.

Have I made some mistake that can explain the observed behaviour?

(Btw, I think maybe the “Check this box to be notified of replies to this topic.”-box is not working, since I have not received any notifications from my earlier posts.)