column balancing question

[Michal Kvasnicka <quasar@econ.muni.cz>]

Good morning.

One reason for me to switch to ConTeXt were its macros for typesetting 
in columns that are highly superior to any such macro I have ever seen. 
(I typeset almost all my documnts in two columns.) But I am not able to 
supress one strange feature: some pages are one more line longer than 
they should be. It happen randomly -- or at least I was not able to find 
out when it happens. Therefore I'm not able to prepare an minimal file. 
I thougth that setting
\widowpenalty=0
\clubpenalty=0
\brokenpenalty=0
\normalbottom
may help, but it does not.

Can you tell me how to fix this very problem? Well, it does so on all 
versions of ConTeXt I have ever tried and both with teTeX and TeXLive 
distribution.

Many thanks for your attention and help.
Yours
Michal Kvasnicka

P.S. my document setting is like this (some example can be found at 
http://www.econ.muni.cz/~qasar/tmp/delba_prace.pdf):

% output=pdf
\setupbodyfont[ss,10pt]
\setuplayout
[topspace=2cm, height=fit, lines=55,
backspace=15mm, width=fit,
margin=0pt,
header=3\baselineskip, footer=0pt,
grid=yes]
\setuppagenumbering[location=]
\setupheader[style={\em}]
\setupheadertexts[Axel Leijonhufvud: Jednotlivec, trh a průmyslová
dělba práce][pagenumber]
\setupindenting[medium]
\indenting[first]
\setupfootnotes
[location=columns, rule=off,
before={\blank[3*line,small]}, after=]
\setupfootnotedefinition
[location=left,width=fit,
sample={\mathematics{\star\star\star}\ },hang=1]
\setupcolumns[balance=no]

\widowpenalty=0
\clubpenalty=0
\brokenpenalty=0

\setuphead[section]
[number=no, style={\bf},
before={\blank[3*line]}, after={\blank[line]},
indentnext=yes]