Not really familiar with Mac, but I do know Linux. If they're as similar as I think they are (both based on UNIX and inherit a lot from it), then this might be the same thing.
The home folder must match the name of the user that owns it. Lots of things are hardcoded with that assumption. And the settings/configuration/etc. are of course included in the user's home folder, so that different users can have different settings.
Change it back, and it'll probably work. If you really want it to be different, change the username (much bigger deal), and the home folder *should* follow automatically. It might be easier to create a new user with the correct name, then copy and chown (change owner) everything from one home folder to the other, and then delete the old user and home folder. Probably easier done as root, or with sudo all over the place.
