Running processes, htop and gnome-system-monitor

I had a minor issue with SMPlayer (suddenly no sound, and random crashes), and checked the running processes and found three and I killed them using gnome-system-monitor, but they didn’t disappear. So I checked htop, and could not find the process id:s, so I restarted gnome-system-monitor and searched for SMPlayer again, and the three processes are still there?

This does not seem normal to me? I did just upgrade to the latest stable a few hours ago, I am not sure it is related to that though. I am sure the problem will go away, at least for a while, if I restart the machine, but my question here is really about the difference in reporting running processes between htop and gnome-system-monitor. I have never seen that before, but maybe there is an explanation for that?