Comment 1 for bug 716819

Not sure, but needs proper consideration for sure.

SBCL considers unknown-at-the-moment types pretty much as if they were SATISFIES types involving an unknown function.

This may be a divergence, and if so it needs to be either fixed or documented (and a rationale given.) If it turns out the be allowed, it should still be documented because I don't think you're the first person to wonder about this...