\starttext

  $T^a_b^c$ 

  $T^a{}_b{}^c{}$

\stoptext

produces (unless my eyes are deceiving me) twice the same output, with the subscript b below a. 

One possible workaround is to add 0-width spaces after indices (I just added this workaround to the wiki so that it shows one working option). This seems a bit of a hack, though (and not the easiest to type with most keyboards), and the results are not perfect (the space between the a and c looks a bit too wide to me; although that is probably subjective, and can be resolved by manually adding \kern s). 

Would anyone know if there is a better (easier to type and/or producing a better result without having to manually add negative \kern s) solution? 

Cheers,
Florent