Just doing a quick search in the 1850 Slave Schedule, I see there was a Nancy Maultsby that owned slaves in Bladen. Wm Q and Josiah Maultsby owned slaves in nearby Columbus county, and David S and John S Maultsby were in Cumberland county.
The 1860 Slave Schedule shows Josiah, John A and Carver Maultsby as large slave owners in Columbus County.
I see Stephen Maultsby's race was listed as "black" in the 1870 and 1880 censuses. It was not uncommon for someone to be shown as mulatto in one census and black in another.