On Wed, Mar 26, 2008 at 9:23 PM, Hans van der Meer
Wolfgang,
From your observation I am inclined to guess that the \ifx falls prey to the collection of arguments. The \relax can be replaced by an extra pair {} behind the description: \answerblock{}{}% also typesets without the if-error.
You could also add "title=no" to \definedescription[answerblock], this stops TeX from looking after a optional argument between the braces.
I more or less conclude that the lookahead from \dodoublegroupempty does not stop on the \if. If I remember correctly, that behaviour is to be expected from tex and the prospects for solving it generically within the format bleak. If Hans Hagen is listening, can he comment on this?
I tried your module also with my ancient ConTeXt from august last year and it did also show this effect. Your module is broken since a very long time. Wolfgang