unread status lost when topics are moved

When a topic is moved from one forum to another, none of the forums_track or topics_track informaiton is changed. That means that the unread status of the moved topics as well as the unread status of the source and destination forums may be incorrect after the move.

I doubt there is a fix that would be efficient enough to be practical so long as phpbb3 sticks with a forums-based unread tracking system. (A fix would, I think, require code that would check individual flags for each and every user and update that user's forums_track and topics_track entries as appropriate for that user...which can be done but I think would drag down a board).

If phpbb3 were to move to a topics-based rather than forum-based unread tracking system (like ptirhiik's unread flags mod did for phpbb2), that would solve the problem for moved topics at the cost of some hit to efficiency (I don't have a feel for how much that hit would be).

By the way, I came accross this bug as I was thinking about the bug reported here: http://www.phpbb.com/bugs/phpbb3/15729 . That bug was reported more than a year ago but is marked as new and unassigned. If someone gets assigned to look into that bug, they may want to take a look at the fix I posted for it here: http://www.phpbb.com/community/viewtopic.php?f=70&t=1357705