envdte and pkgdef : unable to load file or assembly when searching .exe

Hello,

I want to use some Wpf windows and viewmodels from a Wpf application inside my vspackage.

I know about pkgdef rootfolder tip and how to embed a library in my vsix.

The problem occurs when I want to use a mainWindow, the debugger tells "unable to load file or assembly" probably because of .exe.

If I switch the wpf application to ClassLibrary,  then it is working perfectly.

Is it possible to use a window from an exe in a vspackage instead of a dll because I don't want to rewrite my big wpf app ?

Thanks in advance for your help.

(To reproduce just add a wpf application project, sign,add as reference to  your vspackage and show mainWindow initialize)

(Check pkgdef too)

Edit: if I put the wpf.exe in PrivateAssemblies folder, it is working. I suspect VS2012 to have a kind of filter somewhere to search only .dll in  $rootfolder$ but not .exe