I reproduced this on a multi-screen Windows 98 machine. May also happen on 2000 and/or ME.

* start SwingSet
* drag the SwingSet window onto a secondary monitor
* switch to the ComboBox demo
* pop-down the "Philip, Howard, Jeff" ComboBox - it appears above the tab, instead of below it
* drag SwingSet back onto the primary monitor
* again, pop-down the first ComboBox. This time it appears even FARTHER above the tab - it isn't even attached.

Switching to another demo and then back to the ComboBox demo apparently fixes this (until you do it again).