Steps to reproduce:

This is reproducible in the Explorer demo ( Simply go to the basic form demo and on the DateField marked "Birthday", click the button that shows the DatePicker (this gives focus to the text field), then hit Tab.

Actual Result: DatePicker remains on screen even though another field has focus.
Expected: DatePicker hides.

Tested in IE7 and latest Safari 3.2.1. This bug is NOT reproducible in Firefox (last version I checked was 3.0.6).