[NTG-context] partial derivatives with bonum/pagella font

Hi all, The following examples give wrong space. There is a space between the prime and the subscripted x. If I do not load the bonum font it just looks as it should. \setupbodyfont[bonum] \starttext $f'_x$, $f_x'$ $f\prime_x$. \stoptext (it does not look good with the pagella font either...) Any ideas? /Mikael