Collaborative Completion glitch

[Ukase]

On Praetor Duncan's first mission in Dark Astoria, I thought it might be interesting to see if I could teleport Duncan to the waypoint. I couldn't - got an invalid target message. No worries, left the character with teleport at that spot. 

Proceeded to escort Duncan to the waypoint on the map. 

Left my third account idle at the door/manhole cover. 

When the mission ended, all three characters exited. The two that were by Duncan and Diabolique - their missions completed. The one idle by the door - that character's mission did not complete. And yes, all three characters had Collaborative Missions enabled. 
 
My guess is if your character isn't by Duncan at completion (or maybe Diabolique, or maybe both) then you won't get credit for completing it. 
Given the nature of the bug, (if it's a bug), it will take me another week or so to try and replicate it. 

I offer this as more of an FYI than anything else.