(This appears to be the same issue which was raised by Alexandros 
Frantzis in October 2008; see the thread at 
http://www.mail-archive.com/ntg-context%40ntg.nl/msg32125.html. No 
resolution was proposed at that time, and the problem still exists.)

Extra whitespace occurs before itemizations and tabulations (and quite 
possibly other structures) which appear immediately following an 
in-margin heading. The following example illustrates this.

    \setuplayout [backspace=7cm,leftmargin=6cm]

    \setuphead   [chapter][]

    \setuphead   [subsection]
                  [alternative=normal,command=,distance=1em]

    \setuphead   [subsubsection]
                  [alternative=normal,command=,distance=1em]

    \setuphead   [section][distance=0pt,
                   alternative=text,
                   command=\MarginHead]

    \define[2]\MarginHead{\inmargin{#1 #2}}

    \startbuffer[Item]
       \startitemize
         \item Item
         \item Idem
       \stopitemize
    \stopbuffer
    \startbuffer[Table]
       \starttabulate[|l|l|]
         \FL\NC Entry \NC one \NC\NR
            \NC Entry \NC two \NC\NR\LL
       \stoptabulate
    \stopbuffer

    \starttext

    \chapter{Itemize}

    \section{No extra whitespace}
    With text here there is no extra whitespace before the itemization.
    \getbuffer[Item]

    \subsection{No extra whitespace}
    With text here there is no extra whitespace before the itemization.
    \getbuffer[Item]

    \section{Extra whitespace}
    \getbuffer[Item]
    With no text before the itemization there is extra space after the
    heading.

    \subsection{No extra whitespace}
    \getbuffer[Item]
    With no text before the itemization there is extra space after the
    heading.

    \chapter{Tabulate}

    \section{No extra whitespace}
    With text here there is no extra whitespace before the table.
    \getbuffer[Table]

    \subsection{No extra whitespace}
    With text here there is no extra whitespace before the table.
    \getbuffer[Table]

    \section{Extra whitespace}
    \getbuffer[Table]
    With no text before the table there is extra space after the heading.

    \subsection{No extra whitespace}
    \getbuffer[Table]
    With no text before the table there is extra space after the heading.

    \stoptext

Is this unresolvable? Like Alexandros, I have tried many of the options 
that looked appropriate, but nothing seems to work.

-- 
Rik Kabel