[Xmonad] Java app doesn't want to display itself in xmonad

Hey all, I've got a java app I want to use called JabRef for tracking research papers (http://jabref.sourceforge.net/), but whenever I try and run it while using xmonad I just get an empty grey window - it doesn't crash, it just seems to sit there. I tried starting it in KDE, and it started up successfully, so I can rule out a java install problem. Has anyone else had problems with Java apps (or maybe even this one) in xmonad ? Cheers Dave