on linux, with the "compose" input method, some dead keys are not working

On a linux fedora 23 system using kde which is configured with greek (polytonic) keyboard, there are some dead keys which are working and other which are not working. In particular, keycode 47 (the ; on a us keyboard or the m on a french keyboard) is mapper to "dead_acute", and the same keycode shifted is mapped to "dead_abovecomma". The expected behaviour is to have

dead_acute + Greek_alpha => U03AC
dead_abovecomma + Greek_alpha => U1F00
dead_acute + dead_abovecomma + Greek_alpha => U1F04

For all the Qt5 applications I have tested, the dead_acute key is working as expected, but the dead_abovecomma is not (it seems to be ignored). Applications which are not working include kf5 kde applications (konsole, kate, dolphin, plasma) and qdbuviewer-qt5.

All the other applications I have tested get all the dead keys right. Applications which are working include xterm, firefox, libreoffice, non-kf5 kde applications (kmail, gwenview, konqueror) and qdbusviewer (the qt4 based one).

I insist that qt4 applications are working, but not qt5, so this is a regression. I took the example of the dead_abovecomma key, but there are other non-working dead keys.

In case it is relevant: my system is configured for a french keyboard, with some keys to switch dynamically to the greek(polytonic) keyboard.