Changing surnames

I have come across an interesting situation with one branch of my family the baptism record and marriage record show my 2nd great grandmother as Maria Matilde Medel (born 1833 in San Miguel el Alto, Jalisco, Mexico) with her parents as Ygnacio Medel and Maria Pabla De Los Dolores Almaguer and her husband as Bernardo Reynoso.

When I was checking the baptism records of their children some of the actual records have Matilde's and her father's and grandfather's last name as Lampon.

Three questions, has anyone else come across situations like this and why would they use different last names in records and the third question does anyone have any information on the Lampon family in Los Altos area?

Thanks for any and all information.