OK, I have investigated, and I see what's wrong. The ABSOLUTE-PATHNAME slot of COMPONENT acts like a kind of cache (it's filled by resolving the RELATIVE-PATHNAME), but it is not being cleared when the system is reloaded.
I have a proposed patch that involves a REINITIALIZE-INSTANCE :AFTER method on COMPONENT, and it seems to fix the problem. I am just finishing up a test case (as usual, the bugs in the test script are harder to find than the bugs in ASDF!), and expect to push a fix tonight or tomorrow morning.
cheers, r