I have the following WPF Window: http://uploadffs.nl/images/2015/09/09/Untitled.png
I am unable to click the folder if the mouse is on the blue window, note that the window is set to "Topmost".
I have noticed that setting the background to transparent, I am able to click anything underneath the window.
Code:
<Border BorderThickness="1" Opacity="0.5" CornerRadius="50,50,0,0" BorderBrush="Black" Background="#FF5A9AE0"/>