When display contrast is set to 100%, disabled JavaFX menu items get completely invisible. I haven't tried Caspian, but this bug is definitely reproducible with Modena. Setting com.sun.javafx.highContrastTheme to blackonwhite doesn't help.

The bug is reproducible with 1.8.0 and 8u20-b23 (where RT-36692 is integrated). Doesn't look like a regression, most likely it's been there forever.