course/recent.php (in 1.5)

which has been moved to:

course/report/outline/index.php (in 1.6)

creates invalide HTML because it wraps the tables in a ul tag without any containing li tags.

It's fairly simple to make it validate, though it might take some thinking to do 'the right thing' accessibility/semantic-wise which might involve even more table markup e.g. one big table broken up into sections per topic/week.

See question 4 in this post for more info:

http://moodle.org/mod/forum/discuss.php?d=45944