Paint Job Problem

Is it possible that the box you stored it is was by a window or door that allowed the UV rays of the sun to hit it. Or was there a time that he was on a layout that would have the suns rays cast upon it?

Um, no.

First of all, I didn't made my first layout for it's run. Because I don't have any more tables/room/spaces to build one.

Second, I kept it in my smaller eco-box under my bed for a long time, until I got my new and larger eco-box to store more of the tracks.

Third, I didn't left any of my locos near my window.