In the following program (and attached), even though a key value in a KeyFrame is altered, the behavior of the Timeline is not affected. This used to work, and I first noticed the issue in the SDK 1.3 b27 partner release. Thanks! Jim Weaver.

/*
 * MetronomeDynVals.fx - A simple example of animation using a Timeline
 * with dynamic KeyFrame time and values.
 *
 * Developed 2009 by James L. Weaver jim.weaver [at] javafxpert.com
 * as a JavaFX Script SDK 1.2 example
 */
package projavafx.metronome.ui;

import javafx.animation.KeyFrame;
import javafx.animation.Interpolator;
import javafx.animation.Timeline;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.control.Slider;
import javafx.scene.input.MouseEvent;
import javafx.scene.shape.Line;
import javafx.scene.shape.Rectangle;
import javafx.scene.layout.HBox;
import javafx.scene.paint.Color;
import javafx.stage.Stage;

var durMs:Number = 1000;
var xVal:Number = 100;
var yVal:Number = 50;
var endXVal:Number = 300 on replace {
  println("endXVal is now:{endXVal}");
};
var endYVal:Number = 50 on replace {
  println("endYVal is now:{endYVal}");
};
var anim = Timeline {
  keyFrames: [
    KeyFrame {
      time: 0ms
      values: [
        xVal => 100,
        yVal => 50
      ]
    },
    KeyFrame {
      time: bind 2000ms - (durMs * 1ms)
      values: [
        xVal => endXVal tween Interpolator.LINEAR,
        yVal => endYVal tween Interpolator.LINEAR
      ]
    },
    KeyFrame {
      time: bind (2000ms - (durMs * 1ms))*2
      values: [
        xVal => 100,
        yVal => 50
      ]
    }
  ]
  repeatCount: Timeline.INDEFINITE
};

Stage {
  title: "Metronome Dynamic Values"
  visible: true
  scene: Scene {
    width: 400
    height: 500
    content: [
      Rectangle {
        width: 400
        height: 500
        fill: Color.TRANSPARENT
        onMousePressed: function(me:MouseEvent):Void {
          endXVal = me.x;
          endYVal = me.y;
        }
      },
      Line {
        startX: bind xVal
        startY: bind yVal
        endX: 200
        endY: 400
        strokeWidth: 4
        stroke: Color.BLUE
      },
      HBox {
        layoutX: 60
        layoutY: 420
        spacing: 10
        blocksMouse: true
        content: [
          Button {
            text: "Start"
            disable: bind anim.running
            action: function():Void {
              anim.playFromStart();
            }
          },
          Button {
            text: "Stop"
            disable: bind not anim.running
            action: function():Void {
              anim.stop();
            }
          },
          Slider {
            min: 100
            max: 2000
            width: 500
            value: bind durMs with inverse
          },
        ]
      }
    ]
  }
}