I can't reproduce your issue.
sbcl --eval '(require :asdf)' --eval '(trace compile-file load asdf::perform sb-ext:run-program)' --eval '(require :sb-posix)'
sbcl --eval '(require :asdf)' --eval '(trace compile-file load asdf::perform sb-ext:run-program)' --eval '(asdf:load-system :sb-posix)'
Both work fine for me.
What ASDF configuration do you use?
Could it be that you're running from a dumped image and that you're not exporting SBCL_HOME to a proper value? ASDF does something magic with SBCL_HOME for those output files.
But yeah, I shall submit a patch to SB-GROVEL so that things should work even in screwy cases like that.
Note that you don't need to define a ASDF-LOAD function now that ASDF has ASDF:LOAD-SYSTEM.
[ François-René ÐVB Rideau | Reflection&Cybernethics | http://fare.tunes.org ]