Symbolic link not working

We have a subdomain with Drupal v6.4. Images for one of the modules display with URL:

Note the empty directory. I don’t know when this started and I don’t think we loaded anything to cause this to fail. The actual path to the data on the server is:

That avatar_selection directory is actually a symbolic link which goes to a lower level directory which is used to support other sites and subdomains. The idea is to have a single directory with all avatars that’s shared among sites - rather than duplicating thousands of image files for every site. So note that instead of seeing the name of the symbolic link that we simply get two consecutive slashes.

Is anyone else having an issue with Drupal and symlinks? Anything going on with the servers?
I had an issue with symlinks a couple months ago, which turned out to be a FileZilla bug. This is different. I can cd from ./files to avatar_selection at shell with no problems. I can hardcode the full URL and see it in a browser.

I’m guessing there is something in Drupal (is_dir(), is_writable()…) that tests to see if a directory is writable or accessible and it’s failing. I don’t know if that’s a Drupal bug or something in our environment causing normal PHP code to fail.