I tried opening a udev .rules doc with Kate editor and it wouldn’t load, so I persisted a few times trying a few other .rules and got the same. I gave up and used Kwrite.
Thought nothing of it until I’m booting frequently to test something, and as I’m logging in every time, the missing Kate editors appear (empty) - like 6 or 7 of them 
They won’t go away, they are haunting me at login. lol!
Thanks.
Set “Start with an empty session” in Configure Desktop->Startup and Shutdown->Session Management.
Or try to kill kate, it might hang and therefore get recorded by the session management to be restarted even though you already closed it. If it is not running at logout it should not get restarted either.
Done start with empty session, but will flip it back later and see if it replicates.
Do you know if session restore restores text in documents, or just the apps that were there??
Depends on the application, as it’s the application’s job to save/restore its state.
In general, the open documents should be restored, but unsaved changes rather not.
And there’s a bug/incorrect behaviour in Qt5 which causes Qt5 (or KF5) based applications often not being restored at all (because they quit too early and are not running any more when the session manager records the applications to restore on the next login).
PS, I just read this:
https://mail.kde.org/pipermail/release-team/2015-December/009227.html
So Kate indeed does not quit correctly at the moment, and keeps on running if you close its window.
This is a bug in Kate.
It just didn’t happen before because KDE Frameworks5 had another bug that compensated this, but that one got fixed in 5.17.0, causing the problem with Kate to surface.
So I take it that you installed Frameworks5 from the KDE:Frameworks5 repo?
Should be fixed in Kate 15.12.0, which will be available on Wednesday in KDE:Applications, and sent as update to Leap 42.1 afterwards.