Bug#803423: #803423 libqt5gui5: Ugly GUI (no icons) / Weird interpretation of XDG_CURRENT_DESKTOP and GNOME_DESKTOP_SESSION_ID

[Vladimir K <pzs-fs@yandex.ru>]

I was able to get qt applications to show icons with qt5ct application and plugin (which is apparently quite slow and heavy, at least judging by speed of related stdout messages).
So, from my point of view the essense of this bug currently is that qt5 fails to get GTK icon theme when gtk-related environment variables are set, which it should do without any additional plugins like qt5ct. 
If GTK2_RC_FILES and QT_STYLE_OVERRIDE are properly set, Qt should get both theme and icons. Currently it gets the theme right, but fails on icons.