Playing around I discover that this is acceptable:
\begin_inset FormulaMacro
\newcommand{\bmath}[1]{\mathbf{a}}
But this isn't:
\begin_inset FormulaMacro
\newcommand{\bmath}[1]{\mathbf{#1}}
The font-specifier is dropped in the case of macro-arguments.
Regards,
Angus
