This issue is related to JFXC-2651. If the compiler is fixed so that it statically detects wrong comparisons (e.g. a == b, where a is of type A and b is of type B where A and B are unrelated types) javafxgui fails to compile with the following message:

 [javafxc] /usr/local/home/maurizio/Desktop/fx/franca/javafxgui/src/com/sun/stylesheet/javafx/PaintConverter.fx:199: incomparable types: com.sun.stylesheet.css.parser.Token and String
  [javafxc] inverseSplit = paint9Bounds.getFirstToken() == "inverse";
  [javafxc] ^
  [javafxc] 1 error

The compiler complains because a String cannot be compared to com.sun.stylesheet.css.parser.Token (the result of the comparison would be always false!).

I checked the code - the offending bits seems to be related to an unused flag called 'inverse' split. Removing it makes the problem go away.