Program: 33535
Project: 33535
Buggy source:
private static void tickStart(){
  if (mc.thePlayer != null) {
    boolean flyState;
    boolean descendState;
    if (SJConfig.customControls) {
      flyState=mc.inGameHasFocus && Keyboard.isKeyDown(flyKey);
      descendState=mc.inGameHasFocus && Keyboard.isKeyDown(descendKey);
    }
 else {
      flyState=mc.gameSettings.keyBindJump.getIsKeyPressed();
      descendState=mc.gameSettings.keyBindSneak.getIsKeyPressed();
    }
    boolean forwardState=mc.gameSettings.keyBindForward.getIsKeyPressed();
    boolean backwardState=mc.gameSettings.keyBindBack.getIsKeyPressed();
    boolean leftState=mc.gameSettings.keyBindLeft.getIsKeyPressed();
    boolean rightState=mc.gameSettings.keyBindRight.getIsKeyPressed();
    if (flyState != lastFlyState || descendState != lastDescendState || forwardState != lastForwardState || backwardState != lastBackwardState || leftState != lastLeftState || rightState != lastRightState) {
      lastFlyState=flyState;
      lastDescendState=descendState;
      lastForwardState=forwardState;
      lastBackwardState=backwardState;
      lastLeftState=leftState;
      lastRightState=rightState;
      PacketHandler.instance.sendToServer(new MessageKeyboardSync(flyState,descendState,forwardState,backwardState,leftState,rightState));
      SyncTracker.processKeyUpdate(mc.thePlayer,flyState,descendState,forwardState,backwardState,leftState,rightState);
    }
  }
}

Fixed version (ground truth):
private static void tickStart(){
  if (mc.thePlayer != null) {
    boolean flyState;
    boolean descendState;
    if (SJConfig.customControls) {
      flyState=mc.inGameHasFocus && Keyboard.isKeyDown(flyKey);
      descendState=mc.inGameHasFocus && Keyboard.isKeyDown(descendKey);
    }
 else {
      flyState=mc.gameSettings.keyBindJump.getIsKeyPressed();
      descendState=mc.gameSettings.keyBindSneak.getIsKeyPressed();
    }
    boolean forwardState=mc.gameSettings.keyBindForward.getIsKeyPressed();
    boolean backwardState=mc.gameSettings.keyBindBack.getIsKeyPressed();
    boolean leftState=mc.gameSettings.keyBindLeft.getIsKeyPressed();
    boolean rightState=mc.gameSettings.keyBindRight.getIsKeyPressed();
    if (flyState != lastFlyState || descendState != lastDescendState || forwardState != lastForwardState || backwardState != lastBackwardState || leftState != lastLeftState || rightState != lastRightState) {
      lastFlyState=flyState;
      lastDescendState=descendState;
      lastForwardState=forwardState;
      lastBackwardState=backwardState;
      lastLeftState=leftState;
      lastRightState=rightState;
      PacketHandler.instance.sendToServer(new MessageKeyboardSync(flyState,descendState,forwardState,backwardState,leftState,rightState));
      SyncTracker.processKeyUpdate(mc.thePlayer,flyState,descendState,forwardState,backwardState,leftState,rightState);
    }
    JetpackParticleType jetpackState=null;
    ItemStack armor=mc.thePlayer.getEquipmentInSlot(3);
    if (armor != null && armor.getItem() instanceof ItemJetpack) {
      Jetpack jetpack=((ItemJetpack)armor.getItem()).getJetpack(armor);
      if (jetpack != null) {
        jetpackState=jetpack.particleToShow(armor,(ItemJetpack)armor.getItem(),mc.thePlayer);
      }
    }
    if (jetpackState != lastJetpackState) {
      lastJetpackState=jetpackState;
      SyncTracker.processJetpackUpdate(mc.thePlayer.getEntityId(),jetpackState);
    }
  }
}