Import the attached jar that brings ThermostatView custom component.
Drag from Custom section of Library a ThermostatView on Hierarchy or Content.
Drag back from either Hierarchy or Content the ThermostatView to the Library ==> you get the stack below, no update of Custom section is taken.

Mar 14, 2014 11:07:41 AM com.oracle.javafx.scenebuilder.app.SceneBuilderApp$SceneBuilderUncaughtExceptionHandler uncaughtException
SEVERE: An exception was thrown:
java.lang.NullPointerException
at com.oracle.javafx.scenebuilder.kit.editor.panel.library.LibraryPanelController.processInternalImport(LibraryPanelController.java:715)
at com.oracle.javafx.scenebuilder.kit.editor.panel.library.LibraryPanelController.access$200(LibraryPanelController.java:102)
at com.oracle.javafx.scenebuilder.kit.editor.panel.library.LibraryPanelController$5.handle(LibraryPanelController.java:579)
at com.oracle.javafx.scenebuilder.kit.editor.panel.library.LibraryPanelController$5.handle(LibraryPanelController.java:572)
at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:86)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:54)
at javafx.event.Event.fireEvent(Event.java:204)
at javafx.scene.Scene$DnDGesture.fireEvent(Scene.java:2920)
at javafx.scene.Scene$DnDGesture.processTargetDrop(Scene.java:3146)
at javafx.scene.Scene$DnDGesture.access$6400(Scene.java:2896)
at javafx.scene.Scene$DropTargetListener.drop(Scene.java:2860)
at com.sun.javafx.tk.quantum.GlassSceneDnDEventHandler$3.run(GlassSceneDnDEventHandler.java:89)
at com.sun.javafx.tk.quantum.GlassSceneDnDEventHandler$3.run(GlassSceneDnDEventHandler.java:85)
at java.security.AccessController.doPrivileged(Native Method)
at com.sun.javafx.tk.quantum.GlassSceneDnDEventHandler.handleDragDrop(GlassSceneDnDEventHandler.java:85)
at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleDragDrop(GlassViewEventHandler.java:586)
at com.sun.glass.ui.View.handleDragDrop(View.java:683)
at com.sun.glass.ui.View.notifyDragDrop(View.java:998)
at com.sun.glass.ui.mac.MacPasteboard._putItemsFromArray(Native Method)
at com.sun.glass.ui.mac.MacPasteboard.putItemsFromArray(MacPasteboard.java:143)
at com.sun.glass.ui.mac.MacPasteboard.putItems(MacPasteboard.java:165)
at com.sun.glass.ui.mac.MacSystemClipboard.pushToSystem(MacSystemClipboard.java:223)
at com.sun.glass.ui.SystemClipboard.flush(SystemClipboard.java:51)
at com.sun.glass.ui.ClipboardAssistance.flush(ClipboardAssistance.java:59)
at com.sun.javafx.tk.quantum.QuantumClipboard.flush(QuantumClipboard.java:274)
at com.sun.javafx.tk.quantum.QuantumToolkit.startDrag(QuantumToolkit.java:1150)
at javafx.scene.Scene$DnDGesture.dragDetectedProcessed(Scene.java:2940)
at javafx.scene.Scene$DnDGesture.process(Scene.java:3009)
at javafx.scene.Scene$DnDGesture.access$8400(Scene.java:2896)
at javafx.scene.Scene$MouseHandler.process(Scene.java:3762)
at javafx.scene.Scene$MouseHandler.access$1800(Scene.java:3471)
at javafx.scene.Scene.impl_processMouseEvent(Scene.java:1695)
at javafx.scene.Scene$ScenePeerListener.mouseEvent(Scene.java:2486)
at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:314)
at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:243)
at java.security.AccessController.doPrivileged(Native Method)
at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:345)
at com.sun.glass.ui.View.handleMouseEvent(View.java:526)
at com.sun.glass.ui.View.notifyMouse(View.java:898)

Mar 14, 2014 11:07:41 AM com.oracle.javafx.scenebuilder.kit.library.user.LibraryFolderWatcher exploreAndUpdateLibrary
INFO: Start exploring JAR /Users/yjoan/Library/Application Support/Scene Builder/Library/ThermostatView.jar