Aha! There is no difference in Permissions, but the working recent-
files file isn't "hidden" but the one generated originally by IDLE was.
If I make the one I made "hidden" then IDLE stops working again.
The .idlerc folder has been hidden all along though - that doesn't
affect it.
If anyone's changing the way IDLE writes these files, would it be worth
me saying that aesthetically, I'm not a fan of it putting them in a
hidden folder in my top level User folder. What about putting them down
inside Users/AppData like other applications do? Just a thought.