Fonts in konsole window sporadically get distorted

The fonts in konsole window sometimes gets distorted. Most often only the tab text is distorted as in this image: Distorted tab

But sometimes the whole window is distorted: Distorted window

The distortion happens when the mouse pointer leaves or enters the window, or when switching tabs. This problem is present for some time now, unfortunately I do not know when it appeared.

Other programs are not affected.

What can be the problem?

The system is a Dell Latitude E7470 (Intel Iris 540 graphics) running Opensuse Tumbleweed, KDE Plasma 5.11.4, Frameworks 5.40.0, Qt 5.9.3. The xf86-video-intel is 2.99.917.770_gcb6ba2da-1.2 (2.99.917+git781.c8990575-1.1)