This happens in my game, not sure if it's everyone's game, but I own a Feltzer and a Surano for Michael inside his safehouse garage. EVERYTIME I take the Feltzer out, and mod it, OR just drive it, it duplicates the same Feltzer in the impound overwriting my Zion or Sultan. Of course, I am not fool, so I don't save it when this is the case.
The Surano can be touched and doesn't duplicate into the impound and the other two characters, Trevor and Franklin, don't duplicate either, only that Feltzer in Michael's safehouse.
Anybody else run into such a problem? Pretty soon I might as well trade the Sultan for the Feltzer inside his safehouse garage, and just leave that blasted Feltzer inside the impound since it has a mind of its own and seems to like going to the impound.
No other vehicle has done this to me, only that Feltzer in Michael's safehouse.