Inside window page, user control's popup problem WPF

Do correct me if I did not understood your requirement properly.

 

You are showing a small window in a popup, in that when user click on OPEN button, an openFileDialog is opening and when it is opened, the popup seems disappear. Right?

 

If yes then, I think that no need to bind with StaysOpen property, let it be true, so that when openFileDialog is opened, the popup should remain open. To manage the popup to open and close when all your work done, you can use popup.IsOpen= true/false as required (as mentioned earlier).

 

Is there any reason to choose popup control and show that form in it. Instead you can directly show that window.

 

Nevertheless, if it not the issue, do let me know.