Hi folks, I've used SolveSpace for years but I'm always learning something new. For example, on this project I learned that I'd overlooked the documentation on constraining angles equal, which saved me some construction geometry I've had to do before.

My employer recently got a FDM 3D printer and uses it enthusiastically to make fixtures and tools for our weird processes. This is the first time I'm making a part to be actually fabricated, rather than checking fits or planning a mechanism. This project is a vacuum cleaner attachment for cleaning a set of air circulation louvers that we're supposed to clean periodically but currently can't.

I'm posting because I tried to exploit the 3D printing process by putting in cool retention clips on a mating part and pockets for them on this part. I wanted an array of three or four down each side. However, when I try to cut the pockets, the part loses watertightness/oreintability if the cut occurs on _a certain portion_ of the faces where I want it.

The part flips out when any vertex of the cutting object moves aft of the angled construction lines marked with pennants in the attached assembly. On one side, the locations are slightly different if the cutting object is imported versus cutting with a native sketch-on-workplane. On the other side, they're apparently the same.

There's no urgency; I'm just going to go with "Well, don't do that then!" and leave out the last clips. The tool probably doesn't need all these clips in the first place and we can always drill and pin it in minutes if necessary. I'm just asking you experts if there's something obvious I did wrong. I've had SolveSpace blow up before, but always in reasonable circumstances like trying to intersect three curved surfaces or at mechanical singularities in a mechanism. This part has some moderately mean stuff with angled cuts through extruded arcs, but where the problem appears to happen is just an extrusion into an extruded segment. But maybe that goes wrong sometimes too and I just haven't had it before.