Some of Italian provinces (states) has no cities - getCitiesOfState(countryCode, stateCode)

[liudrinschieugen]

Some Italian states short codes contain strings with numbers and letters. When I specify a string with numbers in the method getCitiesOfState I get an array with cities, but when I specify a string with letters the array of cities is empty.
I.e. '26' returns an array with the cities data, 'TG' returns an empty array.
Any thoughts?