Current behaviour:
If you want for the Prophet 6 arpeggio to sync to midi clock, you have to go into globals and change the clock mode.
However, now you can't use the arpeggio when there's no midi clock. Then you have to go into globals once more, and change it back.
Future behaviour:
Auto-clock (maybe a new globals setting). Meaning, if there's midi clock present, the arpeggio will sync to that. If there's no midi-clock present, the arpeggio will sync to the internal clock.
All of the above could apply to the sequencer as well.