the stylesheet containts a class definition for sideBoxContent to apply the bottom border in the form of a background image..

The "support center" sidebox does not define a DIV with the above class...and thus does not apply the background.. you will need to modify the template for the support center box and look for the following line below the javascript...

<div style="clear: left;"> </div>

and change it to

<div class="sideBoxContent"> </div>

hope this helps, as I have not seen that particular contribution...