Comment 3 for bug 659931

This is an appmenu related issue. And java apps are usually not supported unless they use the native GTK toolkit.

In this case, the solution is to disable appmenu for the application you need to start:
(from the command line)

$ UBUNTU_MENUPROXY= tuxguitar (or whatever the application name is)

To permanently disable appmenu for tuxguitar, the easiest way is probably to unset the UBUNTU_MENUPROXY env. variable directly in the wrapper script that is used to start the java application itself.