Got the stack below while using SceneBuilder 2 on FX 8 b117, Ubuntu 12.04, hardware acceleration ON.
Seems harmless, and didn't manage to reproduce.
I log it for reference, will add details later if I manage to get some useful one.

Exception in thread "JavaFX Application Thread" java.util.ConcurrentModificationException
at java.util.HashMap$HashIterator.nextNode(HashMap.java:1427)
at java.util.HashMap$EntryIterator.next(HashMap.java:1461)
at java.util.HashMap$EntryIterator.next(HashMap.java:1459)
at com.sun.javafx.collections.ObservableMapWrapper$ObservableEntrySet$1.next(ObservableMapWrapper.java:588)
at com.sun.javafx.collections.ObservableMapWrapper$ObservableEntrySet$1.next(ObservableMapWrapper.java:576)
at com.sun.javafx.scene.KeyboardShortcutsHandler.processAccelerators(KeyboardShortcutsHandler.java:340)
at com.sun.javafx.scene.KeyboardShortcutsHandler.dispatchBubblingEvent(KeyboardShortcutsHandler.java:168)
at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:54)
at javafx.event.Event.fireEvent(Event.java:204)
at javafx.scene.Scene$KeyHandler.process(Scene.java:3867)
at javafx.scene.Scene$KeyHandler.access$2100(Scene.java:3814)
at javafx.scene.Scene.impl_processKeyEvent(Scene.java:1992)
at javafx.scene.Scene$ScenePeerListener.keyEvent(Scene.java:2449)
at com.sun.javafx.tk.quantum.GlassViewEventHandler$KeyEventNotification.run(GlassViewEventHandler.java:170)
at com.sun.javafx.tk.quantum.GlassViewEventHandler$KeyEventNotification.run(GlassViewEventHandler.java:123)
at java.security.AccessController.doPrivileged(Native Method)
at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleKeyEvent(GlassViewEventHandler.java:197)
at com.sun.glass.ui.View.handleKeyEvent(View.java:517)
at com.sun.glass.ui.View.notifyKey(View.java:927)
at com.sun.glass.ui.gtk.GtkApplication._runLoop(Native Method)
at com.sun.glass.ui.gtk.GtkApplication.access$200(GtkApplication.java:48)
at com.sun.glass.ui.gtk.GtkApplication$6$1.run(GtkApplication.java:149)
at java.lang.Thread.run(Thread.java:744)