I don't have a facebook account to test this so I'm not sure what that area is supposed to look like (though I agree that looks weird). But in the absence of other replies to this thread I want to suggest that you try a default style to ensure it's not a problem with your custom style.
1) Try to reproduce the problem on a default style. Create a new style with no parent:
Admin CP -> Appearance -> Styles -> Create New Style
Then select that style on your forum. If the problem goes away when using the new style then you know it's a problem with your custom style.