This happens to be the top padding plus the bottom padding on the element id f3c. I have attached two pics – one of IE8 and one of IE9.
I tried to capture the relevant information from the debugger. Basically I have a link inside a fieldset, inside a form. The fieldset is so the page validates.
I’m using relative positioning for the link (top:9px).
Not sure why IE9 would add in in 4px from IE8’s calculation unless for some reason it is counting the (padding-top:2px and padding-bottom:2px).
ACTUAL DOCTYPE
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">


Based on the screenshot, you’re adding padding to an inline element.
Try adding:
And make the adjustments from there.
edit:
Inline elements don’t apply margin/padding/width/height (well they shouldn’t but browsers like ie have non-standard behaviours)
Block elements can have margin/padding/width/height but they cause elements to be stacked vertically.
inline-block is kind of a hybrid between them. They allow other inline elements to be placed vertically next to them, however you can also add margin/padding/width/height to them.
My general rule is that block level elements are the heavy construction elements in a page (the framework) where as inline is for the content within the page (bold, italics, etc). inline-block allows you to fudge inline elements a little with the margin, padding.
note: Just be aware that in older versions of ie this still isn’t pixel perfect.