Common guys, read my posts! I have said twice that I do not have the issue now, so how can I do what you are asking for?
I did open the lock, on the last file that had that issue, deleted days ago.
Can't remember exactly, but I did click on the gear and remember seeing the
"Make me the owner" greyed out, indicating I was already the owner.
If and when I get the issue again I will try running ls -l on the affected file. (Hope I never get the chance) as suggested by Kilamite.
(Edit with new info) I had a TextEdit file open, made no changes to it, just reading it as I used easyFind to search for a file, and suddenly got a popup with, in effect, "You do not have permissions to save this file".
The popup had a highlighted "Save anyway" button and I remember clicking on that - and getting the strange custom permissions later previously. This time I just cancelled out and quit TextEdit without saving. The file still had correct permissions! So obviously the issue is not with the file, but rather the system's automatic save function and somehow the system can't access the destination folder. Where does TextEdit save its automatically saved files?
I noticed Onyx has a delete automatically saved files option in the cleaning pane, so there must be a separate folder somewhere for that.
Ah, the mystery deepens .....