I'm pretty sure it's Linux. I'm able to chmod my files for my Backup User.
Or are you talking about your .snapshots directory? If so, then you can't alter anything in there. It's essentially Read-Only.
Speaking of that Backup User, initially, I was on the backup2 server. Without warning or notice, I'm on backup3. (I just checked Support History, and not a peep) Too bad I still can't rsync.