This tells me that there's a bug in your OS's Java implementation. Is it by any chance Windows? Maybe Linux? When popups like menus or tooltips are "heavyweight", Java creates them in their own windows (as implemented by the OS). When they're "lightweight", Java tries to avoid making new windows if, as is the case for the Layers popup, the menu stays within the boundaries of an existing Java window. In that case, Java fakes it by drawing them using Java graphics in the original window. Ignoring the bug you're seeing, generally speaking lightweight popups are more efficient. So why doodon't heavyweight? Because in Display3D they don't work. So why do them in Display2D? Because some people -- like myself -- actually have simulations with windows which contain both Display2D and Display3D. Sean On Aug 7, 2012, at 10:19 AM, Andrew Reilly wrote: > So I tried setting that parameter to true as you suggested: > > popup.setLightWeightPopupEnabled(true); > > ...and it worked!! > > Thanks for that. > > Now the big question...why?