KDE restarts properly closed programs

KDE has a very nice feature called “Restore previous session”. The trouble is, it restarts some programs that were closed and I’m sure they were closed. For example, it recently began to restart Dia after each reboot, but I closed it properly right now and rebooted the computer. It’s up again.

No, it’s not in autostart anywhere. No, my option is “Restore previous session” and not “Restore manually saved session”. Any ideas why some programs get stuck no matter what?

I know that I can add programs to exclude list, but that’s kinda backwards.

Ubuntu 20.04, KDE framework 5.68.0, but I think this behavior started an year or two ago.