According to the rules for an end tag of "dd", "dt" or "li" at:
implicit end tags should be generated for previously unclosed tags until the matching "dd"/"dt"/"li" is found. In the case where there's a structure like:
where XX is one of these tags WebKit nests the second XX and its children inside the first <div>. It should close out the first <div> at the first </XX> tag.
Created attachment 28246 [details]
Testcase for <dd> <dt> and <li>
The DOM structure is wrong for all three pairs of tags. The rendering for <dt> looks valid, but the rendering for <dd> has incorrect indentation and the rendering for <li>s has overlapping numbers.
FF3 has the correct DOM structure in all three cases and renders the <dd>s correctly but makes the same rendering mistake on <li>s.
Here is a real-life example of this bug.
Firefox closes the div correctly and doesn't trigger the bug.
This bug is fixed by the HTML5 parser.