I hope I can explain what's happening...
using vista and xl2007, but same thing happens in xp and xl2003.

I have a pair of option buttons on a worksheet that are yes/no answers to a
question. They are ActiveX option buttons. They have the same group name
and behave normally in that when you click the one for yes, the linked cell
changes to true (same for no). If yes is true, and you click no, then yes
changes to false and no changes to yes (works the other way around also).

The weirdness is that when you click the option button, and the linked cell
changes, the button itself does not appear to be clicked. And that's not
all! Generally if you click yes, then click yes again it just remains
clicked. These buttons, if you click yes, then click yes again then it
changes the linked cell to false the second time. This same behavior happens
with the no button.

I've searched in the code, and no part of the code refers to these cells or
option buttons.

I've got a number of sets of yes/no option buttons on the sheet and none of
the have the same problem. I tried deleting the buttons and inserting new
ones, and deleting and copying from another set on the sheet, but as soon as
I change the linked cell it reverts back to the strange behavior.

Has anyone seen this before? Even better, anyone have any ideas as to how
to fix it?

Hope that makes sense