There are two problems with WPF windows when the WindowStyle=None option is used.
I have a nice quick and dirty solution. Try following code when maximize your none bordered window:
if (WindowState == WindowState.Normal)
{
WindowStyle = WindowStyle.SingleBorderWindow;
WindowState = WindowState.Maximized;
WindowStyle = WindowStyle.None;
}
The trick is to set the WindowStyle to SingleBorderWindow then maximize the window and set it back to None.