Until this problem is fixed in the official code release, it can be fixed by editing /plugins/wp-forum/forum-functions.php line 666:
Original:
$visit = "<span><br />You last visited: ".date(get_option('forum_date_format'), get_usermeta($user_ID, 'lastvisit'))."</span>";
Updated:
$visit = "<span><br />You last visited: ".date(get_option('forum_date_format'), get_usermeta($user_ID, 'lastvisit')+0)."</span>";
The change is the addition of “+0” near the end of the function call. Be sure to place it within the correct set of parentheses.
