Wrong comment character after newline

Hi,

I use ConTeXt with the \asciimode setting. That means the comment
character is %%, instead of %. I set commentstring to %% %s.
However, when I start a new line in a comment, only one percent sign
is inserted, instead of two followed by a space:

%% Foo<CR>
%
^ (cursor)

I'd like to have it like this:

%% Foo<CR>
%%
^ (cursor)

What option is responsible for the string that is inserted after a
newline is started in a comment? It does not seem to be related to
commentstring.

Marco