Can't remove group type form Group once a Group type has been selected

If you create a group and select for it to be an Access control group or a Mailing list group then your group will always be one or the other.  You can't change the group settings so that it is neither.

eg Set the group type to Access Control, then edit the group settings you can untick the access control box, but when you click on Save the group is still an access control group.   

You can change the group type from Access control to Mailing list or vice versa but you can't set it to have no group type.