[NTG-context] Double-sided documents with MetaFun's Field[Text][Text]

[śrīrāma]

Dear list,

I have a double-sided document in which I want to draw certain page 
backgrounds on the right (odd) and left (even) pages. Here is an example

%%% SOF
    \setuppagenumbering[alternative=doublesided]
    \setuplayout
            [backspace=4cm,
            leftmargin=4cm,
            cutspace=2cm,
            rightmargin=2cm,
    leftmargindistance=0cm,
    rightmargindistance=0cm,
                header=2cm,
                footer=2cm,
            topspace=1cm,
            bottomspace=1cm,
                    top=1cm,
                bottom=1cm,
                width=middle,
                height=fit]

    \startuseMPgraphic{page}
    StartPage;
        draw Area[Text][Text] 
            shifted (InnerMarginWidth,BottomHeight+FooterHeight);
        draw Field[Text][Text] withcolor blue;
    StopPage;
    \stopuseMPgraphic
    \defineoverlay[page][\useMPgraphic{page}]
    \setupbackgrounds[page][background=page]

    \starttext
    \dorecurse{10}{\input knuth \page}
    \stoptext
%%% EOF

In the resulting PDF the Field[Text][Text] path is not positioned (/computed?) 
correctly, while the manually positioned Area[Text][Text] path is as expected. 
So, it seems that the margin widths and other distance are updated for each 
odd, even page but Field[Text][Text] is still wrong? The Field[Text][Text] 
path appears on every page as though it is on an odd (right) page.

Have I missed something?

Thanks,
śrīrāma (Sreeram)