(please correct me if I chose the wrong component)
So simply put - build a Qt5 app (with some line input or whatever) , start it , change the layout - system-wide it changes , but the app continues using the layout it was started with . (all that in GNOME . In XFCE for example it doesn't happen) . My system is Manjaro , but I've had the same problem in Ubuntu . That may sound like a gnome problem , but I'm not knowledgeable enough to argue that .
The communication so far - I've made some tests according to the instructions from one of the Qt developers , and one of the GNOME developers stated an opinion that the problem is Qt related . Here's all the posts :
http://lists.qt-project.org/pipermail/development/2013-August/012822.html
http://lists.qt-project.org/pipermail/development/2013-August/012824.html
http://lists.qt-project.org/pipermail/development/2013-August/012827.html
http://lists.qt-project.org/pipermail/development/2013-September/012848.html
http://lists.qt-project.org/pipermail/development/2013-September/012849.html

https://mail.gnome.org/archives/desktop-devel-list/2013-September/msg00046.html

Related bugs according to one of the posts :
https://bugreports.qt-project.org/browse/QTBUG-30911
https://bugs.freedesktop.org/show_bug.cgi?id=23202