By "Family History" password, are you referring to Family Search? If so, did you link your Family Search to your Church Account, or were they separate? Family Search allows you to use your Church account for login; however, I don't know how it behaves when you change your password.
Are you locked out of one of the accounts, or just wondering why the password reverted? If you can't log in, you can try calling the Global Services department for assistance:
https://www.churchofjesuschrist.org/hel ... t?lang=eng