In Wayland sessions on Fedora 24 multi-level window menus are collapsing back to top level spontaneously for gnome applications (e.g. Evolution, LibreOffice, Shotwell).
Steps to Reproduce:
1. open Shotwell
2. in the View menu go to Filter Photos
3. in the expanding submenu, pause the mouse briefly
Submenu stays open until user makes a selection or moves mouse out of submenu
This is a bug in Gtk+, not in wayland protocol itself.
Upstream Gtk+ bug: https://bugzilla.gnome.org/show_bug.cgi?id=768016 is fixed on git master and will land in 3.20.7.
This bug is already fixed in Gtk+ 3.20. Please close this report.