Why is RJTT "Invalid"?

I “forgot the flight number” of an upcoming ANA flight from KPAE to RJTT. I was trying to check if a flight plan had been filed. Ok, that flight plan has not yet been filed, at the time of this post, fair enough.

But what puzzled me is the flight finder grumbles in angry pink with accompanying red X, that “RJTT” is an invalid airport code, though it did guess that I meant the Tokyo area.

So why is RJTT invalid? Is this related to the KHND issue?

If I search for flights between KLAX to RJTT it does find the flights between the two despite claiming RJTT is invalid.


[Edited to add: The flight plan has since been filed as ANA9397]