The clock settings for Sync I/O (and USD) are global and saved within the Pro Tools Preferences as opposed to with the session file. The reasoning is as follows:- If you have a digital console, and your entire studio is resolved to Word Clock (or locked to another source such as Video Ref), and someone brings in a session, Pro Tools should retain the settings of your studio, not the studio from which the session was created. The only exception here is when it comes to sessions employing VSO. As of Pro Tools 5.1.1, the VSO setting was saved as part of the session. In Pro Tools 5.3-5.3.1 the VSO settings are not saved as part of the session.