Not sure if this can be named a bug :-P This issue has to do with tracking forums and the information returned by forum module in this respect. This applies probably to all a.7, 1.8 and 1.9 branches. Not sure in 1.6.

The current implementation in forum_print_overview() just takes care of the current group selected by the user in a course (get_current_group()). See the query at that function:

// bla,bla,bla
$sql .= '(d.forum = '.$track->id.' AND (d.groupid = 1 OR d.groupid = 0 OR d.groupid = '.get_current_group($track>course).')) OR ';

User end up by having diferent number of unread messages in mymoodle and in course page depending on what get_current_group() returns.

Perhaps the implementation should take care of several more things:

. All the groups the user is member of
. If she/he has the 'moodle/site:accessallgroups' capability in that context
. Probably if he/she has the viewdiscussions capability in each forum context

Thanks in advance