Div does not notice when grandparent changes height
Try grabbing the resize widget and resizing *only* vertically. (resize: vertical doesn't work correctly either, filed as bug 15383)
<div style="border: solid; width: 200px; position: absolute; overflow: hidden; resize: vertical; height: 200px;"><div><div style="height: 50%; background: red"></div></div></div>
(In reply to comment #1)
The above is not the same as this bug.
Created attachment 22496 [details]
[WIP] Track and update descendants with percentage heights
Work in progress. May have a significant performance impact.
Although I don't really see anything wrong with the patch, I'm not sure how important it is to complicate the code to fix something that is effectively just a quirks mode problem.
Fixed in <http://trac.webkit.org/changeset/36513>.