If Events.ON_OPEN listener (even empty) is attached to BandBox, the rendering of popup is invalid on ZK7. Unwanted horizontal and vertical scrollbar are added.

bandBox1.addEventListener(Events.ON_OPEN, new EventListener() {
@Override
public void onEvent(Event event) {
}
});

Sample:
http://zkfiddle.org/sample/38rr4fr/1-ZK7-BandBox-ON-OPEN-event-fail