CRM 2013 - Dropdown list is not scrolling

I have a dropdown list that has more items then can be displayed in the section. When I click on the field you see 4-5 items in the list and there is a scroll bar on the right hand side.

The problem is that the control is not active. If you try to scroll down or select an item nothing happens.

If you click on it again it goes away and the if you click on it a third time it drops back down and is now active. At this point you can both scroll and select items in the list

Is this a known problem and is there any fix for it?

Thanks, Gary