I was having this issue as well. The application remained in a "frozen" state and the only other alternative was to load a different LAF.
The suggestion to alter: /etc/java-7-openjdk/accessibility.properties Commenting out: # assistive_technologies=org.GNOME.Accessibility.AtkWrapper Did actually fix the problem. It's hard to say but, this presumably occurred after an update to the JDK. This behavior began approximately two months ago: (Beginning of 12/2015).
