It appears that this issue is specific to IE6, as the code functions correctly in all other browsers.
Check out the jsFiddle link with the HTML code:
<div style="background:blue; width:600px; margin-left:auto; margin-right:auto;">
BLUE
<div style="background:red; position:absolute; width:100%; left:0;">
red
</div>
</div>
Therefore, the "RED" div should fill the entire width of its container (the body in this example). However, in IE6, it stays fixed at 600px. Is there a solution for this bug without resorting to ignoring IE6 completely? (If only we could!)