Now, what to do about the other case... there's still no reason it should bug out, it seems to me. Or rather, it should be implementable in such a way that it shouldn't.
Yes, we do. But if I recall (and I can't test, because the git "wiki" broke for later mzschemes again), apply does work for macros, except it evaluates all the arguments first, which breaks things like and. Someone should test that, though; as I noted, I can't.
I saw, that's how I was able to test. Thank you for setting it up, by the way! And if you fixed it, thank you for that; if someone else did, thank them for that.