Mac: Is preserve corners broken?

I’m sure this should be on the forum somewhere, but I can’t find it.

If I try the “preserve corners” function, it totally breaks the image. Huh?

I’m using Catalina 10.15.4. Doesn’t seem to happen on Windows. Is this related to the fact that the slice tool reduces the image resolution as well on Mac (but not Windows), which I’ve also seen reported?

Bump? Can somebody throw me a bone here? Is it just me that sees this behaviour?