KWin sets a left touch screen edge by default. This feature is problematic for several reasons:
First of all, it doesn't work that well. My wife and I both use Kubuntu 17.10 with Plasma 5.12.x on modern touchscreen laptops the the feature is buggy and unreliable.
Second, its implementation breaks a lot of other workflows and use cases because it's implemented using an invisible single-pixel window tthat runs the height of the left screen edge hat eats clicks and scroll events. This breaks Fitt's Law for any content on the left screen edges and causes a lot of headaches for users, which is the source of a significant amount of bug reports, e.g.:
- https://bugs.kde.org/show_bug.cgi?id=387775
- https://bugs.kde.org/show_bug.cgi?id=386735
- https://bugs.kde.org/show_bug.cgi?id=380476
- https://bugs.kde.org/show_bug.cgi?id=380492
- https://bugs.kde.org/show_bug.cgi?id=380807
- https://bugs.kde.org/show_bug.cgi?id=380957
- https://bugs.kde.org/show_bug.cgi?id=381112
- https://bugs.kde.org/show_bug.cgi?id=384269
- https://bugs.kde.org/show_bug.cgi?id=390654
(Ignore the fact that one is closed; it's still a problem, but the maintainer doesn't think it is)
It also comes up a lot on online support forums and Reddit.
KWin's maintainer has made it clear that this will not be changed or fixed anytime soon:
https://bugs.kde.org/show_bug.cgi?id=390654
The setting will stay enabled by default. This is a maintainer decision! This is a useful feature and we seem to have conflicts here between users expecting it to work exactly like that and users not having a touch screen and having issues with that. In today's world we need to support touch screens by default in a sensible way (e.g. for notebooks) without looking like yesterdays thing. Thus this will stay on.
I recommend that Kubuntu disables this feature. This will require patching KWin, unfortunately. The code responsible is here: https://cgit.kde.org/kwin.git/tree/tabbox/tabbox.cpp#n847