This bug is a Safari only bug (found in Safari 3.1.2 on Mac OS X 10.5.5 using a build from latest 1.1 branch).

To reproduce:
1. Go to the Explorer demo for BorderLayout.
2. Click and drag the resize bar on the east ContentPanel and resize the panel as small as it goes (drag to the right) and continue to drag to the right outside of the browser window without releasing the click.

Actual Result:
The entire app begins to slide to the left and eventually out of view until you release the click on the resize bar.

Expected Result:
Nothing happens.

This doesn't appear in any of the other browsers (did not try Safari on Windows).