\FlushStep does not seem to work when "revealing" steps in a mathalignment.  Is there a known solution for showing rows of a mathalignment in their own "frame"?  Here is the code that I am using:

\usemodule[s-pre-50]
\starttext
    \StartSteps
        \startformula
            \startmathalignment[n=3,align={right,middle,left}]
                \NC a \NC = \NC b + c \NR \FlushStep
                \NC \NC = \NC b - d + d + c \NR \FlushStep
            \stopmathalignment
        \stopformula
    \StopSteps
\stoptext

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