KDE on CentOS steals Alt-Shift from applications?

I'm using KDE on CentOS 7 on one machine and KDE on Kubuntu 16.04 on another.

In both cases I've set Alt-Shift to switch keyboard layout. However, in Kubuntu Alt-Shift-XXX is still free: I can make use of Alt-Shift-5 [aka Alt-%] in Emacs and Alt-Shift-o [aka Alt-O] in Krusader, where as in CentOS all app-specific shortcuts featuring Alt-Shift are broken.

This thread sounds very similar: How to prevent Alt+Shift from switching keyboard layout before keyup?

I need help to research into this issue.