Adding a DOCTYPE,
Code:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
to the reorder.html TreePanel example causes animation of nodes to appear (briefly) outside of the container it occupies. This is somewhat annoying.

To reproduce, add the above DOCTYPE to reorder.html, then expand nodes such that the scrollbar appears. Expand "experimental" node, then collapse it. You should see a brief flash of the child nodes outside of the container while animating. This does not occur in the example w/ DOCTYPE missing.

Observed on IE 6.0 Windows (not tested on others)