I did something causing the -R (--reset-author) switch in the Commit menu to always be on by default. How can I reset this?
As with other Magit popups, set the flags the way you want them to be by default, and type C-cC-c.
(n.b. This is likely how you got into that situation in the first place.)
(or type ?C-cC-c in the popup buffer.)
I can reproduce your problem by setting (default is
(setq magit-commit-arguments '("--reset-author"))
So check this variable in your config, and remove
"--reset-author" from it.