Please read the WHOLE LIST OF COMMANDS I SENT in my test case.
I made the file writable in that list only to modify it. If you read
the whole list of commands, you will see that I make it unwritable
again before editing it with emacs. And that's exactly the
problem... if the file isn't writable, emacs assumes that it's not
checked out and not modified it and checks it out when you hit C-x v
v, overwriting the changes in it.