And tick "Improved Pathfinding" in BGconfig.EXE. It recalculates the path every few seconds. While they still start to wander off, they turn around shorty after to get back on course. (A minor help)

It has not often bothered me though. I've always preferred moving them in smaller groups anyway, using the 7,8,9,0,- keys to select. Or using the follow-the-leader formation where they move out one at a time.

I sometimes HAVE to move them one at a time, otherwise they'll suicide themselves, but it's not a wanted way to get characters from point A to B as it means at least a about 12 mouseclicks instead of 1. Per time you move them. That's a lot of unneeded micromanagement. In relatively open terrain it usually isn't that big of a problem, but in dungeons it's a nightmare. That goes for BG1, and what I've played so far of BG2. It's far from ideal when such issues become a huge thorn in the game's side. Fantastic games of course, but this is a considerable weakness.