Thin ProgressBar doesn't paint properly with Modena Style

My app that is working fin with JavaFX 2.2 uses a ProgressBar where the preferred height (and minimum height) has been set to 5.

It renders in a reasonable way with JavaFX 2.2. using the Caspian style.

On recent builds of Java 8 the progress indicator is not visible, so it looks as if no progress is being made.