I think there is a bug in slime-load-file.
I have noticed that when a file has its *.lisp extension in the parameter to slime-load-file, swank/xref is not able to find its callees (with slime-list-callees).
When called interactively, the extension is stripped and slime-list-callees works. So, shouldn't the extension be stripped by slime-load-file when called non-interactively, as well?
--Jonathan Meeks