Setting a non-NONE 'heightReference' on an Entity's point property causes the billboard to disappear

(https://sandcastle.cesium.com/#c=bVFdT8JAEPwrmz5BglcMEhQq0WCiDyjGr6dLyLVd2ovXvebuCqLhv3ttxfjB2+7szGRnN9FkHawlbtDAORBuYIZWVgV7abAOD5Kmn2lyQhIaHnQnnDi1GobkpJNomUjTzgcngFJbj2ga751mwjhfCRqwldHFFWYG0XaORkM2PBuNRj046bP+4PR00O3VBrFUKtbCpGNoDAFkITIcAw8YC5vahq33cq4zvdRrNEpsWUkZDxqLXa/dRJLbm5TyDdWjfPc+w2YKYVhRoovCRwCXI8So9AZylFnuHnCFBinBPVVQ2pL2y8FakLT51/iP6jv7zW+czeaXt/fLp8Xy+mHxfHfVLstp150EvSCybqtw2mYGuJBFqY2DyqiOD+6wKJXwlwzjKnlFxxJr61fU1Cj8KY1SuQaZnh/4HSRKWOsnq0o11+DBNAo9/59UaZFKyhbtbWtafjydtyBjLAp9e1jptFaxMH+cPwE)

Chrome 118
macOS 14

I expect a point thats set to clamp to the terrain to do so without causing things to vanish.
What happens is it's entity-associated billboard vanishes when its heightReference is set to CLAMP_TO_GROUND or RELATIVE_TO_GROUND

Run the linked Sandcastle reproduction in Chrome on macOS and inspect the Entity point property behavior when heightReference is set to CLAMP_TO_GROUND or RELATIVE_TO_GROUND. Trace the associated billboard handling and verify that the billboard remains visible while the point is clamped to terrain.

Written by the indexing model from the issue text.