Hi Andre, so that is not a bug exactly, it's more of a type of situation that you should avoid.

To have a well formed solid, each edge of the solid must be connected between only 2 surfaces.

In your case the location here there are 4 surfaces touching each other at a single edge:




That forms what is called a "non-manifold" edge in that location. That's problematic for various reasons, it basically makes points on that edge ambiguous for volume oriented calculations.

So you would need to give either a little bit of space or some overlap between your cutting pieces rather than having them exactly graze each other in that manner.

- Michael