The matrix from the following example has an extra row at the end.

=============
\starttext
\startformula
  A = \startmatrix[left={\left(\,},right={\,\right)}]
   \NC 1 \NC 2 \NR
   \NC 3 \NC 4 \NR
  \stopmatrix
\stopformula
\stoptext
=============

I am using mkiv version:
  MTXrun | current version: 2010.07.30 11:35
  This is LuaTeX, Version beta-0.62.0-2010082314

Removing the last \NR fixes the problem, but this is certainly different
from the previous mkiv/mkii behavior.
I wonder this is an intended change, or is it a bug ?

Thanks a lot!

regards,
shenchen