Radio Buttons in Excel 2007 automatically lose the linked cell address

HI
I created a template for Quiz in Excel 2007 and inserted 12 groups of 4 radio buttons in each group ( as I have 12 Questions in my Quiz). I linked the first radio button in each group to a cell. I password protected the file and tried the quiz several times. After a few such file open and saves, I see that a few of the radio buttons have lost their links to the cell that was originally linked. Grateful if some one can advise if the radio buttons lose the value of their linked cell because the sheet was protected or for any other reason/s.

I am using Excel 2007; I first added a group box and ensured that all my four radio buttons from FormControl ( Not Active-x) are placed within that group box and checked they are okay. One of my friends suggested that the linked cells are losing value because I am hiding and conditionally unhiding the rows in which these 12 groups are located. Another friend has suggested that instead of linking to cells , I link to a defined name which points to the cells. Both appear to work well for now. Many thanks.