just now i tried to reproduce it and i couldn't... not with my core file, nor with my standard init files, nor with "sbcl --sysinit /dev/null --userinit /dev/null"
then i tried it from inside slime, our usual dev environment, and it was working there, too for a one or two sbcl restarts. and after it failed for the first time in emacs/slime, i could reproduce it with the noinit from shell. i don't know sbcl internals, but this is quite strange for me!
could it be that based on the loaded dll's or something, sbcl heap is loaded at a different address and there's some identity hash involved in this bug? due to a missing hash function identity hash is used? but i'd better stop making wild guesses... :)
and the backtrace is: http://paste.lisp.org/display/19188