Please, watch the attached video.

Actually there are 3 issues:
1. Scroll bars are not rendered
2. Scroll knob changes its size during scrolling
3. When the arrow of the scroll bar is pressed then exception is thrown

Exception in thread "JavaFX Application Thread" java.lang.NullPointerException
at com.sun.javafx.scene.control.skin.VirtualFlow.positionCell(VirtualFlow.java:1658)
at com.sun.javafx.scene.control.skin.VirtualFlow.adjustPixels(VirtualFlow.java:2030)
at com.sun.javafx.scene.control.skin.VirtualScrollBar.decrement(VirtualScrollBar.java:73)
at com.sun.javafx.scene.control.behavior.ScrollBarBehavior$2.handle(ScrollBarBehavior.java:247)
at com.sun.javafx.scene.control.behavior.ScrollBarBehavior$2.handle(ScrollBarBehavior.java:243)
at com.sun.javafx.scene.control.behavior.ScrollBarBehavior.decButtonPressed(ScrollBarBehavior.java:260)
at com.sun.javafx.scene.control.skin.ScrollBarSkin$3.handle(ScrollBarSkin.java:134)
at com.sun.javafx.scene.control.skin.ScrollBarSkin$3.handle(ScrollBarSkin.java:128)
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.scene.control.skin.VirtualFlow$4.dispatchEvent(VirtualFlow.java:502)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:54)
at javafx.event.Event.fireEvent(Event.java:203)
at javafx.scene.Scene$MouseHandler.process(Scene.java:3543)
at javafx.scene.Scene$MouseHandler.process(Scene.java:3374)
at javafx.scene.Scene$MouseHandler.access$1900(Scene.java:3326)
at javafx.scene.Scene.impl_processMouseEvent(Scene.java:1617)
at javafx.scene.Scene$ScenePeerListener.mouseEvent(Scene.java:2394)
at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:312)
at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:237)
at java.security.AccessController.doPrivileged(Native Method)
at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:354)
at com.sun.glass.ui.View.handleMouseEvent(View.java:514)
at com.sun.glass.ui.View.notifyMouse(View.java:877)
at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
at com.sun.glass.ui.win.WinApplication.access$300(WinApplication.java:39)
at com.sun.glass.ui.win.WinApplication$3$1.run(WinApplication.java:101)
at java.lang.Thread.run(Thread.java:724)