Since the 5.9.2 Plasma update landed the other day, many applications are starting up as pinned to the task manager. It is strangely arbitrary; I haven't yet been able to pinpoint what makes them start as pinned or not. For example, KRDC, Firefox and Thunderbird have all started as pinned but it is not every time I start them, and it is not every application I start. For example, I don't believe Konsole or Dolphin have started pinned (yet). It appears that it will only happen the first time I start the particular application after a fresh boot.
*** This bug has been marked as a duplicate of bug 376572 ***
This was marked as a duplicate, but I get this bug even when I *don't* manually reorder windows/tasks. It also appears to be fairly arbitrary for me too.
For me, the pinning was definitely caused by the reordering, I just hadn't recognized what it was that was triggering it. Furthermore, the fix has come through on openSUSE Tumbleweed, which has resolved it for me. So for my part the bug I was reporting was indeed the duplicate that is now fixed.
Thanks for the reply. Presumably it's something else that I'm doing, so I'll keep an eye on it. The fix hasn't hit Arch yet, but I've just manually patched the file, and see if that fixes all issues. FWIW I can confirm that it fixes the reordering bug at least.