Position: relative and table cells

Hi,

I know this is not the right place for CSS questions, but I’ve a test case that works differently accross browsers and I’m totally unable to say what’s the expected result. The test case is the following one: 

    table {height:50px;}
        tr
            td { position: relative; }
                div { position: absolute; top: 0px; left: 0px; right: 0px; bottom: 0px; }
                    ...

In Opera & Chrome the DIV is sized as I would excect (50px wide, 50px tall)
In IE, it’s positionned just fine, but has no height (50px wide, 1px tall)
In FireFox, the position: relative of the TR is partly ignored (the div takes the whole viewport, but is still z-index-nested in the table cell; that one make no sense).

My question is: Is that behavior expected to be undefined, or should I actually report bugs for this?