[NTG-context] math bold not bold-italic

Hi, I need upright, bold math. Like in this example the lambda: \usetypescript[type-vista.tex] \setupbodyfont[cambria,rm,12pt] \starttext This is \fontname\font ${\bf λ}= 1$ \stoptext But it always gets bold-italic! What is the correct way to get bold math? Thanks, Steffen