Support Forum

As I suspected. For techincal reasons we have to use the same id's for the forum's in-line login form as any other wp login form that may be used. When you have two identical id's this will, sadly, give the double 'check-box' graphic. We can neither change or help that I am afraid.
So I would suggest that the best way would be for you to remove the forum's in-line logion form from the spHead theme template.