Hi Danny, thanks for reporting this bug.

The problem seems to be that the surface normals of that solid are inverted from the way they are supposed to be, that's why it trims away the wrong part of the planes that are extruded from those cutting lines.

When you do a separate and join, the orientation gets recalculated to be correct, so that's why it works properly after that.


Probably the actual bug was unfortunately in some previous step before this point that did not compute the proper orientation...

- Michael