Popup placement in some laptops

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C#

WPF

popup

as you see in following code. I create a popup one time with child and other time without child.

the problem is they open in different places.

note: this happens in some laptops(PC) not all of them.

my laptop = ZenBook model:UX303L (Windows 8.1)

Result Picture

my code:

public MainWindow()
{

    InitializeComponent();
    CreatePopup(true);
    CreatePopup(false);
}

private void CreatePopup(bool hasChild)
{
    Popup popup = new Popup();
    popup.Width = 200;
    popup.Height = 200;
    popup.HorizontalOffset = 500;
    popup.VerticalOffset = 50;

    if (hasChild)
    {
        var tb = new TextBlock() { Text = "TextBlock1", Background =
                                 Brushes.Yellow, Width = 200, Height = 200 };
        tb.FlowDirection = FlowDirection.LeftToRight;
        popup.Child = tb;
    }

    popup.StaysOpen = true;
    popup.IsOpen = true;
}

What I have tried:

this is weird problem and i dont know why.
hope somebody answer me.