unable to rearrange position of Extra Fields in group form

I have added an extra field to the edit form of a Group entity (from the Group module). It displays fine, except that I can't move it. It always shows at the bottom of the form, regardless of how the fields are arranged when I look at the form display configuration page for the group type.

I tried adding the example fields in extra_field_example to "group.*" with similar results. I am able to move the example field on node content type forms, however.

Any ideas what could be involved with why it behaves differently for Group entities versus nodes?