Try the attached. I changed the protection. Removed the Filling in Forms protection
(which in my opinion should seldom be used with anything except legacy forms) and instead selected everything and applied a Group Content Control from the Developer Tab.
Seems to work fine.
The following references may be helpful but do not refer to your problem directly.
If you need password protection (which is not that strong anyway) you could also have it set for No Changes, with exceptions for your option buttons and your Content Controls.