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:

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!