@elreigh Yes, without seeing the actual XML this is just a guess... but by what you described.... the game is trying to create and then subsequently render the image for an "Allied" Arcadia Motor Pool. The game is attempting to change the "Arcadia Motor Pool" into a unit of the Ally, but since the unit is designed as a national specific unit... it is trying to capture the unit as it is defined.
This is not really a bug. I think it is just how you have designed the units. I have come across the same thing while designing.
The other thing that is causing the conflict is that as Allies the game does not view the changing of the territory when the Capital is liberated as a "Capture" strictly speaking.
Would really have to see your XML to figure it out.