What did I do wrong or am I not at all allowed to rename individual buttons? Please advise.

If the optiong group class has a button count > 0, this is exactly what I would expect to happen.

If you want to be able to rename the option buttons in the instance, set the ButtonCount property to 0 in the option group class and set it to the number of buttons you need in the instance. Then you can rename them to whatever you want.

BTW, the same is true for pageframes.