Cannot add a Radio Button to a Form without a choice being added to a previously created radio group

I am working with Acrobat, and want to add several radio button groups to a form. Works fine when i create the first radio button group, after this, when I click on the Radio Button control on the left, it adds a choice to the radio group that already exists? I've tried copying, but get error message saying cannot create multiple copies of this selection. One or more fields in the selection have duplicates in this form. 

This error message makes no sense. There are not duplicates. 

How do I create multiple copies of radio groups? I've tried everything. So far, I have to close down the form, reopen it, then I can add a new radio button group. But, this takes a long time and surely this is not the way it works. 

Thanks ahead of time for help.