Check box gets pre-selected when I save a pdf form as reader extended

Hi,

In InDesign I've created a simple pdf form with 4 check boxes to indicate credit card type.

I've given the check boxes all the same name, so that only one check box can be selected. (They have different values.)

When I export to pdf and preview, everything looks good. None of the four check boxes is pre-selected.

Then, when I save the pdf out as reader extended, one of the check boxes becomes pre-selected (in the on state).

I can't edit the reader extended pdf.

Any ideas?

If it helps, I'm working on an iMac using the Creative Cloud version of InDesign & Acrobat.

Thanks! 🙂