Characters running off into the distance is a Blizzard bug. it occurs on a daily basis and is a potential wiper.
I have posted it on their bug forums like 2 or 3 times now but they continue to ignore it after 2 + years. I even linked to a thread here showing dozens of people who reported it.
I am absolutely positive it is because it occurs in keyclone and in the programs I wrote and I know exactly how they work of course.
Blizzard are just too slack to fix it. My last post to them was not polite but its a real shame that a silly bug like this gets in the way of game play. I think the only way around it is to macro some additional movement keypresses like 5 ms after you break follow. Just enough to counter the bug, but not enough to get in the way of casting.
World of Warcraft - English (NA) Forums -> Follow Bug and running into oblivion