Comment 8 for bug 1306472

After doing a bit more digging over the weekend, I build a debug version of qt from the trusty sources (apt-get source) which included your patches. I had come to the same conclusion that it was something involved with the "Theme Hint", so I think that would be the way to go...

One thing I did note with regard to your comment is that you imply that ubuntu-mono-dark is a gtk2 theme, whereas the new code is using gtk3, but I don't think this is the case. The package ubuntu-mono in trusty, which contains the ubuntu-mono-dark icons:

http://packages.ubuntu.com/trusty/ubuntu-mono depends on http://packages.ubuntu.com/trusty/gnome-icon-theme, which is a gtk3 theme, implied by the fact that it depends on libgtk-3-bin

I don't know if you noticed, but I added a diagnostic label to the project at : https://github.com/GilesBathgate/appmenu-bug

When I run this under QT_QPA_PLATFORMTHEME=appmenu-qt5 ./appmenu-bug The label shows 'gnome'
When I run this under QT_QPA_PLATFORMTHEME= ./appmenu-bug The label shows 'ubuntu-mono-dark'

It might be a good test for your fix to see if with the fix applied both invocations report the same theme (i.e. ubuntu-mono-dark)

Thanks for your work on this.