Launch the attached simple test case:
the application hangs when setting -fx-region-border.

The following exception is raised:

java.lang.ClassCastException: java.lang.String cannot be cast to javafx.scene.layout.Border
at javafx.scene.layout.Region$6.invalidated(Region.java:640)
at javafx.beans.property.ObjectPropertyBase.markInvalid(ObjectPropertyBase.java:111)
at javafx.beans.property.ObjectPropertyBase.set(ObjectPropertyBase.java:145)
at javafx.css.StyleableObjectProperty.set(StyleableObjectProperty.java:82)
at javafx.css.StyleableObjectProperty.applyStyle(StyleableObjectProperty.java:68)
at javafx.scene.CssStyleHelper.transitionToState(CssStyleHelper.java:786)
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.Node.processCSS(Node.java:8732)
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)