Hi,
the original survey is behind a closed network, but I can reproduce (if this is one) the bug.
1 - create a new survey, with just one question of "list radio" kind
2 - give some answers
3 - execute the survey
4 - execute the statistics, there will be a table with the percentages, and a row with "I don't know" 0,00%
U can see my example here:
dl.dropbox.com/u/3198614/p.png
It is that "Non so" - sorry I'm italian
and this is the link:
limesurvey.migrazione.com/limesurvey/index.php?sid=11341
Thanks a lot