This has been verified on Wikipedia, by the way... Istanbul was referred to by a number of different names - Constantinople, Kostantiniyye, Stamboul - until Turkey's government passed the Turkish Postal Service Law in 1930 recognizing only Istanbul, the most common moniker, as the city's official name.
TRANSCRIPTION COURTESY OF JOSEPH HOUK - [1930; The Sultan Ahmed Mosque] (Turkish gentleman) "Well, it's quite simple, actually. Nothing really drastic happened to warrant the switch. We just got tired of the old name, we wanted something a bit more simple. You ever known someone whose name everyone mispronounces? We got it all the time, and it could get frustrating. 'Hey, welcome to Constinopal!' 'Ever been to Cosannapodal?' 'I know a good restaurant in Costanzanoble!' And so on..." (CW) "So they really 'just liked it better that way'... Well, that's another song mystery solved!" (MG) "We're not telling Jimmy Kennedy, right? Because I always liked how They Might Be Giants covered it!"