I've tried to delete those files above and even the whole Config folder, but still the client would reset everything to a non-default setting. Like every time I login, the first game I start would open in window mode, and my custom settings would be reset. Especially, this only happen in my account. If others account login on my PC, it wouldn't happen. I've tried to reinstall the client, but it didn't work.
It's really odd that you're only experiencing this on one account.
Grab Riot's Hextech Repair Tool and check both the box for 'Reinstall' and 'Clean Uninstall', then hit the Start button. This will wipe all files associated with League to ensure corruption doesn't carry over, then reinstalls the game.
Hopefully the this doesn't happen afterwards but if it continues, let me know and I'll direct you to advanced troubleshooting.
I have had that same problem during the last patch and also this patch, also my screen mode switches to windowed.
Keybindings reset when restarting the client for me.
