It's not a bug in MASON, it's some kind of graphics resources allocation bug in Java 1.7.x on Linux distros.  If you fire up your simulation and it displays a large window (typically larger than 500x500), Java will hang badly.  But if you launch some *other* simulation, then use New Simulation... to go to your simulation, everything will work fine.

If you get bitten by this Linux-only bug, here's the workaround we've been playing with.  On roughly line 1806 of sim/display/Display2D.java, there's there's the statement:

        frame.pack();

Replace this with

	final JFrame frame2 = frame;
	SwingUtilities.invokeLater(new Runnable() {
		public void run() {
			frame.pack(); } } );

This should be entirely unnecessary but seems to not tickle the Linux bug.

Sean