Just a guess...
I had some weird Optionbutton behaviour when i set "ShowModal" to
False for that Userform (which, as I understand it, allows the user to
edit content in the workbook while the userform is open.
Unfortunately it also made a lot of my OptionButtons not work - i.e.
the one selected would remain with the value "false" when I clicked my
OK button. I've since set ShowModal back to "True")
I haven't investigated fully why ShowModal does this weird behaviour,
but it's worth looking at from your end I guess