Alkis, now it looks like you're totally and completely right. I have the same experience with the word "арфографии", and I have tested some more Russian mistypes in long words, including both the letters that should work according to your theory, and the letters that shouldn't - and indeed they demonstrate the behaviour you've described.
The only thing that still gets me puzzled is: the mistypes I have used for test while I had Greek dictionary installed are not shown in F7-run, while all the other mistypes I have tested are, no matter what letters they include.
Alkis, now it looks like you're totally and completely right. I have the same experience with the word "арфографии", and I have tested some more Russian mistypes in long words, including both the letters that should work according to your theory, and the letters that shouldn't - and indeed they demonstrate the behaviour you've described.
The only thing that still gets me puzzled is: the mistypes I have used for test while I had Greek dictionary installed are not shown in F7-run, while all the other mistypes I have tested are, no matter what letters they include.