Is it "TURKISH" or "TURKAIR" for THY?

[look_skywatcher]

I'm not sure if this question has already been asked previously. I've tried searching and googling but yiel no satisfactory results.

ICAO DOC 8585 states that the radio telephony callsign for Turkish Airline is
"TURKAIR"

But pilots on the air refuse or even worst ignore when we call TURKAIR. They insist that their callsign is TURKISH.

Is there some background to this that they refuse to be called TURKAIR ?

Thanks in advance.