In the Mobile Project Center extension, why does the checkbox next to TrimbleSessions keep un-checking itself when I save my project?

The checkboxes next to the layers indicate layer visibility.  When you save the project, the Trimble Positions MPC extension will automatically uncheck the entry for TrimbleSessions.  We felt it would provide only minimal value and likely confuse things to have this layer visible in the field and so we hide it by default.  You would see nothing more than the extents of each session if it were visible.  Layer visibility can also be controlled from within the mobile application by clicking Menu…Layer Visibility.