[NTG-context] Context math bug ??

Hi The following does not compile \starttext \startformula [ {\bf{Q}},{\bf {R}} ] = {\bf{Q} } {\bf {R}} - \textbf{R} \textbf{Q} \stopformula \stopttext Error ! Missing \endcsname inserted ....... where as this compiles \starttext $$ [ {\bf{Q}},{\bf {R}} ] = {\bf{Q} } {\bf {R}} - \textbf{R} \textbf{Q} $$ \stoptext Why ?? Kind regards Wim