Tautonyms - i.e., words, phrases, etc. whose spelling is tautological - are of two kinds: terms such as froufrou and Pago Pago, which were fashioned from two or more identical subunits, and terms such as hotshots and valval, which were not. In the first group, tautological spelling is automatic, while in the second group its occurrence is a matter of chance.
"More Accidental Tautonyms,"
Word Ways: Vol. 42
, Article 9.
Available at: http://digitalcommons.butler.edu/wordways/vol42/iss3/9