[NTG-context] \tfa or \bfa etc. doesn't work in math mode

The following example, when process with mkiv, will result in math italic in the first two examples, where it should be roman and roman bold. \starttext $\bfb Hello World$ % doesn't work $\tfb Hello World$ % doesn't work too $\tf Hello World$ % fine $\bf Hello World$ % fine \stoptext -- Khaled Hosny Arabic localiser and member of Arabeyes.org team Free font developer