Tonegod GUI DragElement BUG

Hello, I found a bug tonegod GUI,Use drag DragElement controls 150 times may lead to program crashes
1jpg
2png

Drag the number 150 ,Lead to system crashes, not throw an exception !

`package test;

import tonegod.gui.controls.buttons.ButtonAdapter;
import tonegod.gui.controls.extras.DragElement;
import tonegod.gui.controls.windows.Panel;
import tonegod.gui.core.Element;
import tonegod.gui.core.Screen;
import tonegod.gui.core.layouts.LayoutHelper;
import com.jme3.app.SimpleApplication;
import com.jme3.asset.plugins.ZipLocator;
import com.jme3.input.controls.ActionListener;
import com.jme3.input.event.MouseButtonEvent;
import com.jme3.light.AmbientLight;
import com.jme3.math.ColorRGBA;
import com.jme3.math.Vector2f;
import com.jme3.math.Vector4f;
import com.jme3.system.AppSettings;
import com.jme3.texture.Texture;

public class TestGui extends SimpleApplication implements ActionListener {
Screen screen;
Texture objIcons;

@Override
public void simpleInitApp() {
	assetManager.registerLocator("assets/Gui.zip", ZipLocator.class);

	flyCam.setEnabled(false);
	AmbientLight ambientLight = new AmbientLight();
	ambientLight.setColor(ColorRGBA.White.multLocal(1.4f));
	rootNode.addLight(ambientLight);
	screen = new Screen(this);
	guiNode.addControl(screen);
	guiNode.addLight(ambientLight);

	objIcons = assetManager.loadTexture("exp_5-63182.png");

	Panel panel = new Panel(screen, new Vector2f(10, 10), new Vector2f(250,
			100));
	panel.setIsResizable(false);
	screen.addElement(panel);

	ButtonAdapter grop = new ButtonAdapter(screen, "grop", new Vector2f(5,50), new Vector2f(40, 40));
	grop.clearAltImages();
	grop.setEffectZOrder(false);
	grop.setIsDragDropDropElement(true);
	panel.attachChild(grop);

	ButtonAdapter grop2 = new ButtonAdapter(screen, "grop2", new Vector2f(50, 50), new Vector2f(40, 40));
	grop2.clearAltImages();
	grop2.setEffectZOrder(false);
	grop2.setIsDragDropDropElement(true);
	panel.attachChild(grop2);

	ButtonAdapter grop3 = new ButtonAdapter(screen, "grop3", new Vector2f(100, 50), new Vector2f(40, 40));
	grop3.clearAltImages();
	grop3.setEffectZOrder(false);
	grop3.setIsDragDropDropElement(true);
	panel.attachChild(grop3);

	DragElement drag = createDrag("t","x=40|y=40|w=40|h=40");
	screen.addElement(drag);
	drag.bindToDroppable(grop2);

}

public DragElement createDrag(String id, String iconModal) {

	DragElement dragElement = new DragElement(screen, id, LayoutHelper.position(),new Vector2f(40, 40), Vector4f.ZERO, null) {

		@Override
		public void onDragStart(MouseButtonEvent evt) {
		}

		@Override
		public boolean onDragEnd(MouseButtonEvent evt, Element dropElement) {
			if (dropElement != null) {
				
				return true;
			} else {
				
				return false;
			}
		}
		
	};

	dragElement.setTextureAtlasImage(objIcons, iconModal);
	dragElement.setEffectZOrder(false);
	dragElement.setUseLockToDropElementCenter(true);
	dragElement.setUseSpringBack(true);
	dragElement.setUseSpringBackEffect(true);

	return dragElement;
}

@Override
public void onAction(String arg0, boolean arg1, float arg2) {

}

public static void main(String[] args) {
	TestGui test = new TestGui();
	AppSettings settings = new AppSettings(true);
	settings.setResolution(1024, 600);
	test.setShowSettings(false);
	test.setSettings(settings);
	test.start();

}

}