As shown in the picture when putting a minecart in a frame and looking at any part of the frame it is showing its name "entity.Minecart.rideable.name".

The problem is that that particular minecart is bugged and even in the inventory is known as a "entity.Minecart.rideable.name"

I tried with another "Minecart" never dispensed and no names were showing in the frame.

A normal minecart when shooted by a dispenser and picked up with a pickaxe is renamed to a "entity.Minecart.rideable.name"