Fieldset + Background Image + Uneven Padding = Extra Border Lines

Page Title:

I noticed recently that in IE a fieldset on one of my sites was showing these odd extra "goal post" kinda lines at the top on the left and right.  Basically like the left and right border were extending to the top of the block.  At first I thought it was due to the background image and/or position of the fieldset, as removing the image fixed the problem.  Turns out it was the padding on the fieldset. 

For whatever reason, using uneven left and right padding caused the extra lines.

This is bad (notice the vertical lines at the top of the box):

padding: 10px 5px 20px 20px;
background: #FFFFFF url("img/grnShade.png") repeat-x bottom left;

This is good:

padding: 10px 10px 20px 10px;
background: #FFFFFF url("img/grnShade.png") repeat-x bottom left;

Relevant Tags: CSS