Comment 3 for bug 1819978

You're skating close enough to the edge, I think, that it blowing up only on the third call shouldn't be taken as indicating a bug.

You might try a call to SB-EXT-GC (and also try a call with :full t) between tests to see if the problem still occurs. If it does with the former but not the latter then maybe some garbage is going into an older generation and isn't getting collected soon enough.

Also, is the Mac OS build using the conservative collector? If so, maybe there's a false pointer into that list that's keeping it from being collected.

I think SBCL's design philosophy is to not worry too much about a bit of extra memory usage if that makes GC faster.