I am trying to detach another program's child window using SetParent(hWnd, IntPtr.Zero). After setting parent as null I remove WS_CHILD style. It is OK until I want to change its size, it seems it is acting like a child window still. Only can take up its old container (parent window's client area). Is there a way to change this behaviour in the Windows API?

Here is the code

using System.Runtime.InteropServices;

class Program
{
    [DllImport("user32.dll", SetLastError = true)]
    static extern IntPtr SetParent(IntPtr hWndChild, IntPtr hWndNewParent);

    [DllImport("user32.dll", SetLastError = true)]
    static extern IntPtr FindWindow(string lpClassName, string lpWindowName);

    [DllImport("user32.dll", SetLastError = true)]
    static extern IntPtr FindWindowEx(IntPtr parentHandle, IntPtr hWndChildAfter, string className, string windowTitle);

    static void Main(string[] args)
    {
        IntPtr hWnd = FindWindow("DigiAppWndClass", null);
        if (hWnd != IntPtr.Zero)
        {
            hWnd = FindWindowEx(hWnd, IntPtr.Zero, null, "Edit: test");
            if (hWnd != IntPtr.Zero)
            {
                SetParent(hWnd, IntPtr.Zero);
            }
        }
    }
}

Any help would be great, thanks.