Run Scenebuilder, drag Shapes/Box (FX8) to the content panel, this gets printed in the console:
Dec 22, 2014 7:06:06 PM com.oracle.javafx.scenebuilder.app.SceneBuilderApp$SceneBuilderUncaughtExceptionHandler uncaughtException
SEVERE: An exception was thrown:
java.lang.AssertionError
at com.oracle.javafx.scenebuilder.kit.editor.panel.content.ContentPanelController.scrollToSelection(ContentPanelController.java:380)
at com.oracle.javafx.scenebuilder.kit.editor.panel.content.mode.EditModeController.makeSelectionVisible(EditModeController.java:220)
at com.oracle.javafx.scenebuilder.kit.editor.panel.content.mode.EditModeController.editorSelectionDidChange(EditModeController.java:189)
at com.oracle.javafx.scenebuilder.kit.editor.panel.content.ContentPanelController.editorSelectionDidChange(ContentPanelController.java:789)
at com.oracle.javafx.scenebuilder.kit.editor.panel.util.AbstractPanelController.lambda$new$26(AbstractPanelController.java:231)
at com.oracle.javafx.scenebuilder.kit.editor.panel.util.AbstractPanelController$$Lambda$81/1633047208.changed(Unknown Source)
at com.sun.javafx.binding.ExpressionHelper$Generic.fireValueChangedEvent(ExpressionHelper.java:361)
at com.sun.javafx.binding.ExpressionHelper.fireValueChangedEvent(ExpressionHelper.java:81)
at javafx.beans.property.IntegerPropertyBase.fireValueChangedEvent(IntegerPropertyBase.java:106)
at javafx.beans.property.IntegerPropertyBase.markInvalid(IntegerPropertyBase.java:113)
at javafx.beans.property.IntegerPropertyBase.set(IntegerPropertyBase.java:147)
at com.oracle.javafx.scenebuilder.kit.editor.selection.Selection.incrementRevision(Selection.java:506)
at com.oracle.javafx.scenebuilder.kit.editor.selection.Selection.endUpdate(Selection.java:454)
at com.oracle.javafx.scenebuilder.kit.editor.job.BatchJob.execute(BatchJob.java:128)
at com.oracle.javafx.scenebuilder.kit.editor.job.reference.UpdateReferencesJob.execute(UpdateReferencesJob.java:78)
at com.oracle.javafx.scenebuilder.kit.editor.JobManager.executeJob(JobManager.java:193)
at com.oracle.javafx.scenebuilder.kit.editor.JobManager.push(JobManager.java:82)
at com.oracle.javafx.scenebuilder.kit.editor.drag.DragController.end(DragController.java:127)
at com.oracle.javafx.scenebuilder.kit.editor.panel.library.LibraryPanelController.lambda$startListeningToDrop$262(LibraryPanelController.java:630)
at com.oracle.javafx.scenebuilder.kit.editor.panel.library.LibraryPanelController$$Lambda$146/836936084.handle(Unknown Source)
at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:86)
...

I'm using SB built from the current 8u-dev repo.