Create a new forum disccussion and the record inserted to mdl_forum_read has its discussion field set to 0. This cause that, in the course page, such post isn't counted as unread but, inside the forum page, it shows 1 unread post, when the user has created it!

I think that forum_read->discussion field should be set correctly and, perhaps, an upgrade should be necessary to recalculate all those 0 disccussions...