Recently, I was web developing form on WebView with checkboxes on it and I approach an Exception during using it.
The problem could be reproduced using:
http://download.oracle.com/otndocs/products/javafx/2/samples/Ensemble/index.html#SAMPLES/Web/Web%20View
Please select Web->Web View
Type url: http://jsfiddle.net/Kyswa/1/show/
There should printed huge amount of checkboxes. I've could not seen them all, but that is not the issue. While lively clicking on them (different ones, with ratio 2-3 clicks per second) for few seconds, an exception appears on java console:

Java Plug-in 11.25.2.18
Using JRE version 1.8.0_25-b18 Java HotSpot(TM) Client VM
java.lang.IllegalArgumentException: Image dimensions must be > 0
at com.sun.prism.Image.<init>(Unknown Source)
at com.sun.prism.Image.<init>(Unknown Source)
at com.sun.prism.Image.fromByteBgraPreData(Unknown Source)
at com.sun.javafx.webkit.prism.RTImage.getImage(Unknown Source)
at com.sun.javafx.webkit.prism.PrismImage.getPlatformImage(Unknown Source)
at com.sun.javafx.webkit.UIClientImpl.startDrag(Unknown Source)
at com.sun.webkit.WebPage.fwkStartDrag(Unknown Source)
at com.sun.webkit.WebPage.twkProcessMouseEvent(Native Method)
at com.sun.webkit.WebPage.dispatchMouseEvent(Unknown Source)
at javafx.scene.web.WebView.processMouseEvent(Unknown Source)
at javafx.scene.web.WebView.lambda$registerEventHandlers$32(Unknown Source)
at javafx.scene.web.WebView$$Lambda$270/7446373.handle(Unknown Source)
at com.sun.javafx.event.CompositeEventHandler$NormalEventHandlerRecord.handleBubblingEvent(Unknown Source)
at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(Unknown Source)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(Unknown Source)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(Unknown Source)
at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(Unknown Source)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Source)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Source)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Source)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Source)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Source)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Source)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Source)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Source)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Source)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Source)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Source)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Source)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Source)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Source)
at com.sun.javafx.event.EventUtil.fireEventImpl(Unknown Source)
at com.sun.javafx.event.EventUtil.fireEvent(Unknown Source)
at javafx.event.Event.fireEvent(Unknown Source)
at javafx.scene.Scene$MouseHandler.process(Unknown Source)
at javafx.scene.Scene$MouseHandler.access$1500(Unknown Source)
at javafx.scene.Scene.impl_processMouseEvent(Unknown Source)
at javafx.scene.Scene$ScenePeerListener.mouseEvent(Unknown Source)
at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(Unknown Source)
at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(Unknown Source)
at com.sun.glass.ui.View.handleMouseEvent(Unknown Source)
at com.sun.glass.ui.View.notifyMouse(Unknown Source)
at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
at com.sun.glass.ui.win.WinApplication.lambda$null$141(Unknown Source)
at com.sun.glass.ui.win.WinApplication$$Lambda$36/25551232.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)

The problem is not connected with number of checkboes - I was able to reproduce it with the same stacktrace and 2 checkboxes, but it was harder to do.
After occurring the Exception, there could be some problems with redrawing the checkboxes on form.