This is something I've brought up before but never with a real determination to address the issue myself:

With Qt's default shortcut/action mapping, text editor documents built on KTextEditor are prone to be victim of accidental zooming. Qt's standard for this is Ctrl-Wheel events. This means that systems with a trackpad that use 2-finger scrolling and scroll inertia may cause text zooming when the user holds presses the Ctrl key to trigger a shortcut (say, Ctrl-S to save the current document) before coasting has stopped completely. 

The end of coasting isn't always clear: scroll events may continue to come in with sub-threshold deltas, or when the view has already reached its extreme position and can scroll no further.

Qt itself has a form of protection against this kind of annoyance on Mac and possibly other systems where inertial scrolling has better platform support than under X11. But it's not very difficult to implement a similar protection under X11; a proof of concept designed by Thomas Lübking and me:

https://github.com/RJVB/qtwheeltest/blob/master/wheeltest.cpp

I'd appreciate it if someone could have a look at and comment this approach before I start integrating it with KTextEditor (if at all possible, I haven't checked that yet).