Kiev III/IV crossover model

I have seen two of these in the last five years here in Kiev. A bit of an enigma, maybe the factory was using up the Kiev III bodies or maybe someone requested a Kiev 4 with a foot.
Both models I saw were from 1958, I now own this one. Kiev III and Kiev IV backs are not interchangable so this must be the body of a III

Known examples :

s/n 5825582

s/n 5829479

Known examples