Minecart items ignore builtin/entity parent model and become invisible

The bug

For most entity-rendered items, using builtin/entity as the parent model will cause them to render that entity model in item form. For unknown reasons, this does not happen for minecarts.

How to reproduce

1. Download and apply the attached resource pack
2. Look at a minecart item

Expected results

It would look like a minecart.

Actual results

Completely invisible.