OK, I don't know if this might help, but I found a similar issue elsewhere:
Yes, it's from 1999 and concerns Sybase, but it sure sounds like a similar issue. It also sounds like there was never really a "fix" for the issue.
Not sure if this will help, but it likely won't hurt...
Jason
(PS, I do see on one of my servers in sysprocesses an NTLogin showing a LoginName of SA right now. This is for the "FSAgent Task" which some quick Googleing shows as being used by the FileStream feature (which we are using))