under gnome-session-wayland-session applications with wayland backend menus appear as new windows.

Steps to reproduce:
1. log in to gnome-session-wayland-session
2. activate the gnome-shell-extension "window list" (the one from Classic Mode)
3. start nautilus with X11 backend (default)
4. open and close menus (play with them). you won't notice anything in window list.
5. exit nautilus (terminate all nautilus processes)
6. start nautilus with Wayland backend (via `$ export GDK_BACKEND=wayland nautilus`)
7. repeat 4.

What do I expect to happen:
the same as in 4.

What happens:
I see new "windows" on window list without name or icon for every open menu or sumbenu.

Additional Information:
Tested on F21 Alpha with gtk3-3.14.2. This bug can be reproduced with evolution, evince and others.
This might not be a gtk bug but one in the "window list" gnome shell extension.

While trying to reproduce this bug I triggered these bugs by just opening/closing menus in nautilus / evince:
https://bugzilla.redhat.com/show_bug.cgi?id=1151774
https://bugzilla.redhat.com/show_bug.cgi?id=1151777