Select list and iframes

Hey folks. I have stumbled across a problem and I HOPE this is the right forum to be asking. If not my apologies.
My problem is this: we have select lists displaying in iframes. The iFrame has a vertical scroll bar. If I scroll, the select list appears to stay where it is and doesn't refresh until you either run the mouse over it or click where it should be.
Any ideas as to why this would happen? I've tried using frames instead of iframes and the same thing happens.
Any pointers in the right direction would be appreciated.
Cheers.

Can you post the code for the page or provide a link so we can take a look?