Entities aren't positioned in the center of the minecart while it's slanted

The Bug:

Entities aren't positioned within the center of slanted minecarts.

Steps to Reproduce:

1. Ride a minecart down a slope.
2. Enter third person and observe the position of your model and the minecart's model.

Observed Behavior:

Entities aren't positioned within the center of slanted minecarts.

Expected Behavior:

Entities would be positioned within the center of slanted minecarts.