Compose key doesn't work in qt apps, works in gtk

Using leap 42.1, plasma 5 (5.8.3), the compose key to enter complex characters does not work in qt-based applications like kedit, konsole… but works gtk-based applications e.g in Firefox, gedit etc.
I had this working without even having think about it in 13.2/KDE4 (I did a distribution upgrade). As a workaround, I can install ibus but I don’t understand why I didn’t have to do that in 13.2.

Some values of (relevant?) environment variables as set when I open a konsole:
XMODIFIERS=@im=local
QT_IM_MODULE=xim
QT_IM_SWITCHER=imsw-multi
GTK_IM_MODULE=cedilla

Can anyone help me to figure out why it’s not working (I don’t want to always have that symbol in the systray that shows up when installing ibus)? Thanks!

Systemsettings - Input devices - Keyboard - Advanced
set the compose key to whatever you want from the list ( I use Ralt )

EDIT: some elaboration on why this happens: In 13.2 you ran KDE4, Leap ( and Tumbleweed ) use the KDE Plasma 5 Environment

No, unfortunately, that’s not the cause/solution.
I started systemsettings5 and configured the Compose key; it works in gtk applications, also when I change the position of the compose key, this is respected by gtk applications. But none of the kde applications respect what I’ve set there.

OK, I solved it now (although I don’t know why, really). I had a customized Breeze theme activated. When I changed that to any other theme and then changed back to my customized theme, the compose key started working again – I’m happy!