After opening more than one source window and then trying to close one a stacktrace occurs: java.lang.RuntimeException: requestDeleteInstructionObserver at frysk.proc.dead.DeadTask.requestDeleteInstructionObserver(DeadTask.java:248) at frysk.stepping.SteppingEngine.continueExecution(SteppingEngine.java:607) at frysk.stepping.SteppingEngine.removeObserver(SteppingEngine.java:1095) at frysk.gui.srcwin.SourceWindowFactory$SourceWinListener.lifeCycleQuery(SourceWindowFactory.java:243) at org.gnu.gtk.Widget.fireBooleanLifeCycleEvent(libgtkjava-2.8.so) at org.gnu.gtk.Widget.handleDelete(libgtkjava-2.8.so) at org.gnu.gtk.Gtk.gtk_main(libgtkjava-2.8.so) at frysk.gui.Gui.gui(Gui.java:231) at frysk.gui.FryskGui.main(FryskGui.java:58) WARNING: No task for terminated pid 29125 possibly caused by earlier [test] code failing to clean up all childen WARNING: No task for terminated pid 29124 possibly caused by earlier [test] code failing to clean up all childen There appears to be a problem with the SourceWindowFactory class. It does not appear to handle multiple source windows properly because when one closes it has no clue about which one closed. Seems some smarts need to be added so it knows which source window has been closed and it can clean up properly after it.