If you select text, right click while moving the mouse slightly to the right (so that it overlaps with "cut" on the rightclick menu) it acts as if you clicked on cut and text gets cut
STEPS TO REPRODUCE
1. Select text
2. While moving the mouse to the right and slightly down, right click
3. Text gets cut
The "cut" menu item shouldn't be executed. It can be pretty annoying if you're working fast and you keep triggering this.
KDE Plasma 5.16.3
KDE Frameworks Version: 5.60
Qt Version: 5.12.3
Actually I just realized it happens system-wide. I made a forum post here.
*** This bug has been marked as a duplicate of bug 374311 ***
*** This bug has been marked as a duplicate of bug 410493 ***