Edit: I think found what causes the issue, if you change the colour of the truck to another different than the stock one the issue happen, but if you return the truck to his original colour the issue don't happen.
Hello, I just realized that when you select a curtain on the store if you exit from the garage the curtain no longer matches the model you selected, but if you enter on the garage you can see that the model is the one you selectec, basicaly the curtain only match the selected inside the garage.
I made trials and it looks like the issue don't happen in all the trucks, in my trials i used 3 truks and the Tayga and the Boar has the issue but for example in the Kodiak the curtains are fine.
Greetings and keep it improving the game.