Keyboard won't dismiss even after Focus change

Question

I am creating a Windows 8.1 app and after the user presses a button, a popup opens over most of the screen. There are several textboxes inside the popover.

I found

Answer 1

Please check my answer to my own question:

https://stackoverflow.com/a/24252140/126537

Based on @Paul 's answer. Not very elegant, but works as charm.