Following MWE produces strange output in latest LMTX. mkiv (also latest) output is ok.

\usetypescript[palatino]
\setupbodyfont[palatino,11pt]
\starttext
\m{F_{\rm longIndex}=m_{\rm longIndex}a}
\stoptext

The spacing in the index is wrong.

What am I missing?

Thanks in advance

Christian