windows automatically minimized when using this.Owner

windows automatically minimized when using this.Owner

I have tow windows, main and sub-main the main window have Button, this
Button open the sub-main window the problem is: when i close the sub-main
window, the main the automatically minimized the code of button is:
Sub_Main_window = new Sub_Main_window (new Radio_Station());
Sub_Main_window .Owner = Main_Window; Sub_Main_window
.WindowStartupLocation = WindowStartupLocation.CenterOwner;
Sub_Main_window .Show();