Hey Mark, i found the problem now. After a second very intensive research on google, I found this MDSN article: UIElement.MouseLeftButtonDown Event The problem was that the control didn't captured the MouseButton after the MouseDownEvent because the Mouse probably moved over other object or st. similar. So I captured the mouse on the control:
private void label4_MouseDown(object sender, MouseButtonEventArgs e)
{
label4.CaptureMouse();
}
private void label4_MouseUp(object sender, MouseButtonEventArgs e)
{
label4.ReleaseMouseCapture();
}
That's all. As someone who worked with normal windows forms applications in the past a strange solution but okay. Thanks for the tips and your patience. :) Best regards MyPiano