It’s always nice to find a fix for a Internet Explorer specific bug although not nice the amount of time it takes to find. This particular one relates to setting the height of a <div> containing a background-image which, not unsurprisingly works fine in FireFox.
Which renders thus in IE7:
Note the whitespace beneath the blue image despite this image being 13 pixels high.
Now the solution is as simple as adding overflow:hidden to the divHeight class!
Simple but effective!!