Name tag in mini horse inventory model doesn't billboard properly

When you're accessing the inventory of a horse-like mob with a custom name, it appears above the little entity model.

But as the model turns itself to face the mouse, the name turns with it, rotating about the X axis through 3D space. As a result, it isn't constantly billboarded like names are supposed to be.

Screenshot from 19w46a (even worse 😛)