Show menu via button on another crash Win 8.1 XAML

I have a script in my application where I am showing a popup from a control panel button in Windows 8.x (using XAML / C #). Before Win 8.1 I used Callisto to show the popup. On Win 8.1 I am trying to use the built-in Flyout and MenuFlyout controls.

Simple pop-ups and menu pop-ups work, but when I try to show the drop-down menu that is in the pop-up / pop-up, it rejects the previous pop-up / drop-down image which is not desired.

Here's the code that reproduces the problem:

https://github.com/krishna-nadiminti/FlyoutTest

Any ideas on how to fix this? Ideally - I don't want to go back to using Callisto in a Win8.1 project - because I want to use the same code as part of my framework to display popups and secondary popups in universal apps.