The ARP number used is a global setting. All Parts use the arpeggio number you set.

Each Part will have 8 ARP slots. When ARP #1 is selected - all the Parts with an ARP that is configured to play and is in slot 1 of each Part will sound for the given Part.

If you want say only Part 1 to play an ARP while Part 2 does not - you can set Part 2's ARP slot #1 to Mute 4/4 (assuming 4/4 time signature) which will keep time for Part 2 but play no ARP. An Part 1 will set Slot #1 to any preset Arp you want. Then say you want Arp #2 to have Part 1 and Part 2 playing ARPs at the same time - you would assign the ARP you want to play for Part 1 in Part 1's slot #2 and the ARP you want to play for Part 2 into Part 2's ARP slot #2.

You get 8 different combinations of ARPs and each Part has 8 slots that correspond with the ARPs you want to play for each of the 8 slots.

Thanks Jason. That's my point, the system is set so that selecting an ARP (slot) for a part in a multi part performance will change ARP slot number in the rest of the parts. This means if a performance has different ARPs for each part the user must ensure that they are all lined up in the same ARP slots across the parts, which, as I mentioned in my original post, requires additional menu diving.

I thought reinforcing the description of how it works would help clear up if there were any misconceptions. Maybe there were none.

I know how to work around this

There isn't a workaround to change how this works.

The Problem: once I've selected ARP 7 for Part 2 of the performance the arpegio in Part 1 automatically changes to ARP7.

?

I know how to work around this (by manually selecting the arpegios for each part and having them in the ARP1 slot). But I would still like to know if this is the way the system is set or is this a glitch? The work around does require additional menu diving and therefore additional steps in the workflow.

If you navigate to an individual Part you can review which Arp Types are assigned to that particular Part.

You have a separate overview that shows you what each Part is assigned to do for each of the eight Arp Selects.

Part Arperggio
Select the Part
Press [EDIT]
Touch “Arpeggio”> “Individual”
Here you can see the eight Arp Types assigned to this instrument.

Overview Arpeggio
From the HOME screen
Touch “Motion Control” > “Arpeggio”
Here you can see the 8 Parts and which Arp Type is set to play for Arp Select 1-8... you can view the Arp Type name, when “Category” is selected; you can view the Arp Number, when “Number” is selected; and you can view the Notes that will control/trigger the Arp assigned to each Part, tap “Range”

You just need to know where to look.
Hope that helps.