Seems like the extension is ignored and either lisp or .abcls files are loaded. This means that .asd files are not (an error is thrown) It also means that requests for files that don't exist get satisfied, e.g. if you give it a bogus filetype but there is a .lisp or .abcl file present.
e.g.
(load "jar:file:/Users/alanr/repos/lsw/trunk/patches/test.jar!/bar/bar1.li") ; Loading jar:file:/Users/alanr/repos/lsw/trunk/patches/test.jar!/bar/bar1.li ...
Whoops - there is no bar1.li, just bar1.lisp
(load "jar:file:/Users/alanr/repos/lsw/trunk/patches/test.jar!/bar/bar.asd")
The file #P"jar:file:/Users/alanr/repos/lsw/trunk/patches/test.jar!/bar/bar.asd" does not exist.
Whoops - it does so!
-Alan