> Unfortunately my version of evince doesn't always print correctly  a pdf
> made by context mkiv
>
> \starttext
> $3v$ \par
>
> $3\omega$
>
> \stoptext
>
> When I do print->preview, the math is not shown, and nothing is printed.

  As has already been mentioned, this could simply be a font issue, or a
silly mistake with the way some programs handle Unicode characters with
codes over 65536.