Entity's cooldown timer is reset when the entity touches a nether portal

The portal cooldown timer on the minecart ruins the fun in general.
But that could be happening on some unclear purpose.

But I assume it's resetting every time the cart touches a portal.
Which sounds more like a bug.

Therefore my bruteforce attept on teleporting a cart also doesn't work
(Attached picture)
I would expect the cart to teleport as the 30s cooldown timer runs out, but it never actually teleports.