I have the following:

\starttext

A.
\switchtobodyfont[10pt]{
First published by Stojan Novaković in 1877 in his anthology
\modCyr{\emph{Примери књижевности и jезика старога и српско-словенскога}}  (Belgrade/\modCyr{Београд: Издање и штампа државне штампариjе}, pp.\ 504–505). 

}

\blank[big,fixed]

B.
\switchtobodyfont[9pt]{
First published by Stojan Novaković in 1877 in his anthology
\modCyr{\emph{Примери књижевности и jезика старога и српско-словенскога}}  (Belgrade/\modCyrfn{Београд: Издање и штампа државне штампариjе}, pp.\ 504–505). 

}

\stoptext

This works as expected at 10pt but fails at 9pt (no Russian is printed). The problem does not seem to be with dejavu. 

I have plainly missed something. But what?

Alan