Ever tried to download file via BITS from another user? Don't bother, it won't work. BITS exposes IBackgroundCopyJob COM-interface. And there is AddFile method in it. And it doesn't work for non-logged-in users. BITS has an internal list of logged-in users with tokens corresponding to SIDs. If a user is not in this list, it's treated as error. So if for example we login and start processes, BITS works just fine. But if we try to start process from another user (using API, using runas) and that user isn't logged-in, BITS call will fail.
This issue was found several months ago, it wasn't fixed then. I haven't checked it since, but I suspect it to remain broken for many years to come.