Pool pump turns off after 12 hours

We have a pool with a spa that has a Pentair Intellitouch panel.  We have it integrated with a 3rd party control system using RS-232.  The pool pump is scheduled to turn on at 8am and off at 12am.  This schedule has functioned properly for over 1 year.  Occasionally the pool pump is manually turned on prior to 8am.  When this occurrs the pool pump turns off after 12 hours.  Is there something about turning the pool on manually that defaults to a 12-hour run time?