Created attachment 108371 [details] the menu item when set Global Keyboard Shortcuts -> Plasma (KDE component) Activate Application Launcher Widget. The key is reset upon reboot, or some update now and then, not all reboots cause it to be reset either. I set it to custom - none, as I have phpstorm that uses the combination of Alt+F1. Distributor ID: Ubuntu Description: Ubuntu 16.04.3 LTS Release: 16.04 Codename: xenial
Are you using the KDE backports PPA to get newer Plasma versions, or are you using Bog-standard Plasma from 16.04.x?
Bog-standard
Any chance you can re-test with a more recent version of KDE Plasma, like 5.11.5?
Will test next week.
Well after doing this: https://askubuntu.com/questions/993639/how-to-install-kde-plasma-5-11-on-ubuntu-16-04-kubuntu-16-04 on virtual-box kubuntu 16.04 installation I got in plasma-desktop 4:5.11.5-0neon+16.04+xebial+build79 after going into system settings->shortcuts->global shortcuts->plasma I put the "Activate Application Launchwer Widget" to none. After reboot it was again Alt-F1
*** This bug has been marked as a duplicate of bug 300532 ***