It seems unlikely to me that the issue is a change in Safari. Whatever the problem is, it's something weirder.
A 404 error is generated by the server, not by Safari; changes in Safari should not cause the server to claim that the URL can not be found, unless the server is checking browser agents and has been programmed to spit back a phony 404 error with some browsers.
At this point, you've got me flummoxed.
