[NTG-context] lmmath and \cong

Dear list,
There might be something obviously wrong with the following minimal
example, but it doesn't show the "\cong" symbol.

\enablemode[lmmath]
\starttext
\math{{\cal B} \cong {\cal C}}
\stoptext

I use lmmath to have the same output on calligraphic characters as with latex.

My context version is beta, less than a fortnight old.
Regards,
Chris
___________________________________________________________________________________