Since plasma 5.8, whenever I press Meta (i.e. the Windows key), the "Kickoff" Application Launcher is opened. To close it again, however, I have to reach for the Escape key.
I expect to be able to close the Kickoff by pressing Meta again.
Disclaimer: I've not reproduced this with a clean config
maybe a duplicate of https://bugs.kde.org/show_bug.cgi?id=274914 ?
*** This bug has been marked as a duplicate of bug 367685 ***