Newly Created Groups Not Appearing in Permissions Options?

I post here as a question because I'm not 100% that I haven't missed some setting to make this work.

I am trying to create a new SMB share and set it as belonging to a newly created group. But, any group I create does not appear in the dropdown options. Custom groups that I created before the upgrade to 12 are in the list. But, new ones are not.

Is this a bug? Or, am I missing some flag that allows a group to appear in this list?