Steps to reproduce:
clone SceneBuilder 2, changeset 126b33619c17
Drop a TabPane on Content
Drop a Tab onto the TabPane

On Win you get the crash each time (log attached). On Mac the VM doesn't crash, and on Linux I didn't try.
Note that the NPE in SceneBuilder code will be fixed at some point, and it is likely to mask the underlying issue.

# EXCEPTION_UNCAUGHT_CXX_EXCEPTION (0xe06d7363) at pc=0x7576c41f, pid=6800, tid=2584

Current thread (0x14e41000): JavaThread "JavaFX Application Thread" [_thread_in_native, id=2584, stack(0x15f00000,0x15f50000)]

Java frames: (J=compiled Java code, j=interpreted, Vv=VM code)
j com.sun.glass.ui.win.WinDnDClipboard.push([Ljava/lang/Object;I)V+0
j com.sun.glass.ui.win.WinSystemClipboard.pushToSystem(Ljava/util/HashMap;I)V+90
j com.sun.glass.ui.SystemClipboard.flush(Lcom/sun/glass/ui/ClipboardAssistance;Ljava/util/HashMap;I)V+13
j com.sun.glass.ui.ClipboardAssistance.flush()V+16
j com.sun.javafx.tk.quantum.QuantumClipboard.flush()V+40
j com.sun.javafx.tk.quantum.QuantumToolkit.startDrag(Lcom/sun/javafx/tk/TKScene;Ljava/util/Set;Lcom/sun/javafx/tk/TKDragSourceListener;Ljavafx/scene/input/Dragboard;)V+46
j javafx.scene.Scene$DnDGesture.dragDetectedProcessed()V+63
j javafx.scene.Scene$DnDGesture.process(Ljavafx/scene/input/MouseEvent;Ljavafx/event/EventTarget;)Z+69
j javafx.scene.Scene$DnDGesture.access$8400(Ljavafx/scene/Scene$DnDGesture;Ljavafx/scene/input/MouseEvent;Ljavafx/event/EventTarget;)Z+3
j javafx.scene.Scene$MouseHandler.process(Ljavafx/scene/input/MouseEvent;Z)V+575
j javafx.scene.Scene$MouseHandler.access$1800(Ljavafx/scene/Scene$MouseHandler;Ljavafx/scene/input/MouseEvent;Z)V+3
j javafx.scene.Scene.impl_processMouseEvent(Ljavafx/scene/input/MouseEvent;)V+6
j javafx.scene.Scene$ScenePeerListener.mouseEvent(Ljavafx/event/EventType;DDDDLjavafx/scene/input/MouseButton;ZZZZZZZZZ)V+46
j com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run()Ljava/lang/Void;+422
j com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run()Ljava/lang/Object;+1
v ~StubRoutines::call_stub
j java.security.AccessController.doPrivileged(Ljava/security/PrivilegedAction;Ljava/security/AccessControlContext;)Ljava/lang/Object;+0
j com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(Lcom/sun/glass/ui/View;JIIIIIIIZZ)V+108
j com.sun.glass.ui.View.handleMouseEvent(JIIIIIIIZZ)V+30
j com.sun.glass.ui.View.notifyMouse(IIIIIIIZZ)V+181
v ~StubRoutines::call_stub
j com.sun.glass.ui.win.WinApplication._runLoop(Ljava/lang/Runnable;)V+0
j com.sun.glass.ui.win.WinApplication.access$300(Lcom/sun/glass/ui/win/WinApplication;Ljava/lang/Runnable;)V+2
j com.sun.glass.ui.win.WinApplication$4$1.run()V+25
j java.lang.Thread.run()V+11
v ~StubRoutines::call_stub