IE8 and Opera 10 absolute positioning problems

IE8 and Opera 10 differs to ALL other browsers (FF3, Safari, Chrome, IE6, IE7) in positionin an absolute element inside a div.
If you have something like this:

If you don't put the right: 0px the element won't keep it's original position an will go to the left side of the div becase IE8 and Opera will put default left: 0px if nothing set.
All other browsers will keep a's original position (no left: 0px;)
hope that help to someone.
Keywords: IE8 Opera absolute positioning problem