See video link in URL field for video example. It seems to work just fine when right-licking the desktop, then choosing "Activities". However, using the Desktop Toolbox to try and open the Activities Switcher results in it appearing for only a quick moment, then fading back to the left side of the screen. Reproducible: Always Steps to Reproduce: 1. Click on the Desktop Toolbox 2. Click "Activities" Actual Results: The Activity Switcher opens briefly, then retracts/fades back to the left side of the screen. Expected Results: Activity Switcher to open and stay there. Bug discovered on Kubuntu 15.10 with KDE Plasma 5.5.4 via Kubuntu's backports ppa.
I can confirm this on Plasma 5.6 Beta
It does not happen with the widget explorer, though.
Fixed in http://commits.kde.org/plasma-workspace/b5b3dc08b3f3458680949a2c547ce2ad1282fc47