Its not actually a bug, its done inorder to reduce bugs, in all cases, whenever we buy a new vehicle, all vehicles owned by that player will be refreshed and recreated from database to have bug free usage for players. so thats why its getting refreshed all the time when you buy a new vehicle. As you said, it can be avoided by using /park at the dealer before buying a new vehicle. its a good way to prevent vehicle respawning. Also, this kind of respawn can also be prevented in such a way that trucks get auto parked when user get out from his owned truck, which is close to a trailer dealer for buying the trailer (we will make a special shop for buying only trailers, in the next update). The user will also be infomed about this auto parking after he gets out from his truck for buying a trailer. It will be fixed in next update. Thanks for the info
With Regards
Height