Minecraft minecart duplication glitch- occurs when riding IN a minecart and looking around, especially up;  or from viewing it head-on and then looking up just far enough so when its technically out of view, a second one will appear and disappear when you look back down. It's not actually there, and cannot be interacted with.

It's more of a mild annoyance if anything but should still be considered. Obstructs view if riding in minecart.