What I did was do a join with the Users table to get the correct group value for each post, and had this added to the $tree-array. The way it works now it only checks on $postergroup which is the group for the post you are looking at, which is not the same as what should be shown in the list. Also, inside the show_replies() function it won't even apply as that value is set outside the function.
In 6.2+ the join is already there, so it's mostly a matter of adding U_Groups to the query in all places in both postlist and showthreaded. And passing it along in the $tree array along with all the other values of course.
