There is a hidden option that can be turned on by editing the baldur.lua or by using @argent77's Reveal Hidden Gameplay Options mod. It is called "Enhanced Path Search". From what I can guess, this is an experimental pathfinding option that was added to the game a while ago. What it appears to do is have each character recalculate the shortest path to their destination every few seconds to attempt to constantly find the quickest route. This behavior has some drawbacks over the default pathfinding however. It tends to make your characters turn around if someone else is blocking a narrow walkway at the exact moment that their path gets recalculated. If this is bothering you, I would suggest checking to see if this option is enabled and try turning it off to see if things improve for you. You can turn it off in game with the aforementioned mod installed, or by editing the Baldur.lua located in the documents directory of your game.
In baldur.lua, the option appears as follows if enabled:
SetPrivateProfileString('Game Options','Enhanced Path Search','1')
if it is disabled it will either not appear at all, or appear as follows:
SetPrivateProfileString('Game Options','Enhanced Path Search','0')
