In my data base I have John D.'s father as Thomas Mabe, not Reuben Mabe. I base this on the spelling of the last name also the later location of of the family in Missouri.
I am sure that John is the John Mayab in this census record.
The 1850 Breathitt County, Kentucky census:
Mayab, John (25), Eliza (21), Daniel (2), and William T. (1)
In the same census year there is a John Mabe listed in Hawkins County, Tennessee.
The 1850 Hawkins County, Tennessee census:
Mabe, Elizabeth (22), John (21), and James (1)
whom I beleive is Reuben Mabe's son.
Most of Thomas Mayab's family is listed in the 1850 Claiborne County TN census record, except for one, his oldest. Here is his family's census record
The 1850 Claiborne County, Tennessee census:
Mayabb, Thomas (m,w, 54, farmer, NC), Mary (f, w, 42, NC), Catherine, (f, w, 22, NC), Evaline (f, w, 19, NC), Thomas U. (m, w, 18, NC, laborer), Edward (m w, 16, NC, laborer), Sarah (f, w, 14, NC), Nancy J. (f, w, 9, NC), Hiram (m, w, 8, Va), and Mary A. (f, w, 6, Va)
Before the 1860 census Mary had moved to Greene County, Missouri.
Of course all this is speculation on my part and am open for any comments.