I know it's been a few years since this thread was started. However, I ran into this issue earlier today with my Galaxy S3 and was searching the net for the solution. I actually figured it out on my own, and anyone in the future with this problem; it's easily fixable.
If you find that after syncing FB with your contact list and next thing you know "Mom" becomes "Maryanne Smith-Jones" this is what you do:
Within the contact there should be a Google symbol as well as a FB symbol. When you try to return your mom's name to "Mom" it'll be available via Google, yet FB will still take presidence over the title of the contact. Next to those two symbols there should be a closed link. Click it and unlink the Google contact from the FB contact. Then, from the contact labeled "Mom" link it back to your mother's FB account. Since you're linking FB into Google, it will assume the Google title. If you link the Google title into FB it will assume the FB title.
So to recap.
Mom linking to FB Maryanne Smith-Jones = Maryanne Smith-Jones
FB Maryanne Smith-Jones linking to Mom = Mom
So, if you're like me with creative nicknames for people, unlink them and then link the FB name into the original contact and it will assume the nickname you previously designated.
I hope this helps someone in the future.