Choosing any alternatives on a panel widget (in this case "task manager" or "application launcher") will remove the present widget without adding the new one/alternative. In case of "task manager", any launchers added to it are also removed. Reproducible: Always Steps to Reproduce: 1.Right click "task manager" or "application launcher" 2.Select "alternatives" 3.Choose one.
Thanks. This issue was fixed by [1]. As for the task manager, when applets are exchanged only their shortcut is transfered to the new one, settings are lost. This is a known issue (I can't find the bug right now, though) [1] https://quickgit.kde.org/?p=plasma-framework.git&a=commit&h=1ace6a46dedfb8536890f9c86e7b4fbbc55931ac