Cars - Ford Mustang GT Coupe '65 - Shadow bug when painting '65 Mustang?

Bug Info: Shadow bug seems to appear on livery editor when working on the rear of the '65 Mustang. In the livery editor it seems as you can’t paint / apply layer groups to the middle of the rear of the car, but when you run it on-track those layers show normally. Really odd.

Platform: PC
Edition: Premium
Account: Steam
PC GPU: Not sure. I am running an Acer Nitro 5.
Content Update: Don’t know - I’ve only started painting the car today.