Hi Hraban,

I had a similar problem with math fallbacks (no errors, fallbacks not used) and just found a solution.
Please find a small example below.

I don't understand why we need the line \definefontfamily, but it's necessary for the fallbacks to work.
Also, it stops working when I do \setupbodyfont[mainface,rm].

Cheers,
Jacob

\definefontfallback[cal-fallback][name:modern][uppercasescript,lowercasescript]

\starttypescript[mainface]
  \definetypeface[mainface][rm][serif][palatino][default]
  \definetypeface[mainface][ss][sans] [modern]  [default][rscale=1.075]
  \definetypeface[mainface][tt][mono] [modern]  [default][rscale=1.075]
  \definetypeface[mainface][mm][math] [palatino][default][fallbacks=cal-fallback]
\stoptypescript

\definefontfamily[mainface][math][]
\usetypescript[mainface]
\setupbodyfont[mainface]

\starttext
{\rm \input ward }

{\ss \input ward }

{\tt \input ward }

Should be Palatino: $x + y$

Should be Latin Modern: ${\cal I}$ $\mathcal{I}$ $\mathscr{I}$
\stoptext