[Font] java.util.ConcurrentModificationException

When I run my program, sometimes meet the exception, but I'm not sure how to trigger this bug.
Exception in thread "JavaFX Application Thread" java.util.ConcurrentModificationException
at java.util.HashMap$HashIterator.nextNode(HashMap.java:1429)
at java.util.HashMap$ValueIterator.next(HashMap.java:1458)
at com.sun.javafx.font.PrismFontFactory.getFontResource(PrismFontFactory.java:415)
at com.sun.javafx.font.PrismFontFactory.createFont(PrismFontFactory.java:549)
at com.sun.javafx.font.PrismFontLoader.font(PrismFontLoader.java:177)
at javafx.scene.text.Font.font(Font.java:148)
at com.sun.javafx.css.converters.FontConverter.convert(FontConverter.java:72)
at com.sun.javafx.css.converters.FontConverter.convert(FontConverter.java:42)
at com.sun.javafx.css.ParsedValueImpl.convert(ParsedValueImpl.java:189)
at javafx.scene.CssStyleHelper.calculateValue(CssStyleHelper.java:1429)
at javafx.scene.CssStyleHelper.lookupFont(CssStyleHelper.java:1717)
at javafx.scene.CssStyleHelper.transitionToState(CssStyleHelper.java:612)
at javafx.scene.Node.impl_processCSS(Node.java:8889)
at javafx.scene.Parent.impl_processCSS(Parent.java:1250)
at javafx.scene.control.Control.impl_processCSS(Control.java:872)
at javafx.scene.Parent.impl_processCSS(Parent.java:1281)
at javafx.scene.control.Control.impl_processCSS(Control.java:872)
at javafx.scene.Parent.impl_processCSS(Parent.java:1281)
at javafx.scene.Parent.impl_processCSS(Parent.java:1281)
at javafx.scene.Parent.impl_processCSS(Parent.java:1281)
at javafx.scene.Parent.impl_processCSS(Parent.java:1281)
at javafx.scene.control.Control.impl_processCSS(Control.java:872)
at javafx.scene.Parent.impl_processCSS(Parent.java:1281)
at javafx.scene.Node.processCSS(Node.java:8732)
at javafx.scene.Node.processCSS(Node.java:8725)
at javafx.scene.Node.processCSS(Node.java:8725)
at javafx.scene.Node.processCSS(Node.java:8725)
at javafx.scene.Node.processCSS(Node.java:8725)
at javafx.scene.Node.processCSS(Node.java:8725)
at javafx.scene.Scene.doCSSPass(Scene.java:569)
at javafx.scene.Scene.access$3500(Scene.java:201)
at javafx.scene.Scene$ScenePulseListener.pulse(Scene.java:2385)
at com.sun.javafx.tk.Toolkit$3.run(Toolkit.java:322)
at com.sun.javafx.tk.Toolkit$3.run(Toolkit.java:320)
at java.security.AccessController.doPrivileged(Native Method)
at com.sun.javafx.tk.Toolkit.runPulse(Toolkit.java:320)
at com.sun.javafx.tk.Toolkit.firePulse(Toolkit.java:349)
at com.sun.javafx.tk.quantum.QuantumToolkit.pulse(QuantumToolkit.java:479)
at com.sun.javafx.tk.quantum.QuantumToolkit.pulse(QuantumToolkit.java:460)
at com.sun.javafx.tk.quantum.QuantumToolkit$13.run(QuantumToolkit.java:327)
at com.sun.glass.ui.InvokeLaterDispatcher$Future.run(InvokeLaterDispatcher.java:95)
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$4$1.run(WinApplication.java:112)
at java.lang.Thread.run(Thread.java:744)