It looks like the backgroundLoading else if() content was missed? If not there should at least be a comment why it is not tracked.

diff --git a/modules/fxml/src/main/java/com/sun/javafx/fxml/builder/JavaFXImageBuilder.java b/modules/fxml/src/main/java/com/sun/javafx/fxml/builder/JavaFXImageBuilder.java
--- a/modules/fxml/src/main/java/com/sun/javafx/fxml/builder/JavaFXImageBuilder.java
+++ b/modules/fxml/src/main/java/com/sun/javafx/fxml/builder/JavaFXImageBuilder.java
@@ -63,6 +63,7 @@
             } else if ( "smooth".equals(key)) {
                 smooth = Boolean.parseBoolean(str);
             } else if ( "backgroundLoading".equals(key)) {
+ backgroundLoading = Boolean.parseBoolean(str);
             } else {
                 throw new IllegalArgumentException("Unknown Image property: " + key);
             }