Comment 15 for bug 1307180

"to ensure it's present with pushnew" is precisely what the very last line of asdf/package-system.lisp does.

Unhappily, you subsequently clobber said function.

Instead of wholly clobbering asdf:*system-definition-search-functions*, couldn't you just remove-if from it members of an undesirable subset, i.e. SYSDEF-CENTRAL-REGISTRY-SEARCH and SYSDEF-SOURCE-REGISTRY-SEARCH ? Or, once again, you could (locally) bind *central-registry* to nil and *source-registry* to (make-hash-table :test 'equal).

Since you don't specify what exactly you're trying to do, it's hard to tell how to help.