I think I've tracked this down to e9046da9d3dc1be0aa772c5e7c21b74d1121c350, "Remove unnecessary inline/notinline pairs for defstruct ctors."
That is, the script provokes an error on SBCL 1.3.1.108-e9046da, but doesn't provoke an error on the earlier 1.3.1.107-d503934.
It looks like that commit only changes some inlined-ness of certain functions, so it's probably not the root cause. I'm in over my head.
I think I've tracked this down to e9046da9d3dc1be 0aa772c5e7c21b7 4d1121c350, "Remove unnecessary inline/notinline pairs for defstruct ctors."
That is, the script provokes an error on SBCL 1.3.1.108-e9046da, but doesn't provoke an error on the earlier 1.3.1.107-d503934.
It looks like that commit only changes some inlined-ness of certain functions, so it's probably not the root cause. I'm in over my head.