Cannot change from Contact Sub-type to parent Type

It seems we cannot change a contact who is currently set to a sub-type to go their parent type.

For example, if a contact is an "Individual" with sub-type "Parent", we cannot switch them to just an "Individual (with no sub-type). The form allows the switch in the dropdown, but it does not save the changes properly (the page just goes back to showing the sub-type).

We can, however, change from one sub-type to another. So it seems the form is just not handling the removal/update of contact_sub_type in the civicrm_contact table.