I've noticed that a Russian city of Chaikovskiy refers to "RU.90" region
And this region is absent in admin1Codes.txt file.
So I thought it was error and decided to fix it on geonames by myself.
I navigated to Chaikovskiy and attempted to change the region to the proper value - "Permskiy kray".
The operation failed with the following error
"error while saving:
no code defined for this admin division."
And then I looked at the HTML source for the combo-box. You see the codes are missing for Permskaya Oblast’ and Permskiy Kray.