Maintain state of child window of Experimental instance

Hi

I have one VSIX project. I have added a WPF form to that project for UI .
and set show in taskbar=false for that wpf window.While executing the project, it has been shown in the main window of experimental instance no issues with that. But when i switch over to another window and return back to the Experimental instance window  the wpf window get disappeared.How can i fix this? 

Kani