[tex4ht] is this a bug in tex4ht? Bad mathchar (79119) using \sum with mathml

[Nasser M. Abbasi]

There seems a problem using \sum with tex4ht. I was able to
reproduce it all the time with specific configuration. This
happened when I was trying different configurations to check
some things.

Here is MWE:

----------------------------
\documentclass{article}
\begin{document}
     $\sum F_{x}=m\ddot{x}$
\end{document}
-----------------------

Here is the command to produce the error

     make4ht foo.tex "nma"

here is the error

--------------------------------------
(/usr/local/texlive/2013/texmf-dist/tex/generic/tex4ht/html-mml.4ht)
(/usr/local/texlive/2013/texmf-dist/tex/generic/tex4ht/html4-uni.4ht))
(./foo.aux))
! Bad mathchar (79119).
<to be read again>
                    _
l.6 $\sum F_
             {x}=m\ddot{x}$
?
--------------------------------

Here is nma.cfg which is in the same folder as foo.tex

---------------------------------
\Preamble{xhtml,mathml,ext=htm,charset="utf-8",p-width,pic-align}
\begin{document}
\Configure{$}{\PicMath}{\EndPicMath}{}
\Configure{PicMath}{}{}{}{ class="math" align="absmiddle"}
\EndPreamble
-----------------------------------

If mathml is removed from the above, then no error.

If mathml is now back to the .cfg, but removing the first \Configure
line inside the \begin{document} then the error goes away as well.

Only when mathml and the \Configure{$}{\PicMath}{\EndPicMath}{} is
there, will this error show up.

Using texlive 2013, on linux.

Can someone please verify this and if you think this is a bug and if
I should enter a bug report then.

thanks,
--Nasser