Actually, there is another consideration as well. The townies do everything in a pre-determined order starting in the NW and ending in the SE (at leat I think it's the NW; this may have changed or I might have the directions wrong, but using these directions will work for the example) - for example if you get all the townies in the same place and issue a large order, they will work Southward from the NW corner to the SW corner, go to the Northern end of the next line and work Southward again; continuing until the order is complete. This is not always noticable because the townies often have to travel from far and wide to complete the task; so the work gets done in "patches", but when everyone starts on the same quare it's quite obvious.
I would assume that pathfinding is done in the same fashion. Contrary to popular belief, mobs in Towns try to spread apart from each other whenever possible (the reason sieges clump is because taking the shortest route possible overrides the spreading out behaviour - you'll notice that before they select a target, they spread out quite a bit, and if there is a large open area between them and their target/s they don't clump until right at the last minute, when they all rush the same townie and hence all move towards the same square). This means that if multiple townies want to move along the same path, they will still try not to occuppy the same square unless something with more priority (roads etc.) causes them to. Hence; if they can't all go the same way at the same time without clumping, then some will take the short way and some will take the long way.
The best way to avoid this is to a) have wide paths, b) stagger the orders which cause the townies to move, so only as amny as can fit on the shortest path occupy it at any one time, or c) only have one path and make sure it is paved with the fastest roads possible.
Also, this is true for all versions of Towns, not just 0.47
What's that you're eating? A nice, juicy apple? You weren't supposed to eat that you fool, you were supposed to make it into a pie! - last words recorded words of Francis D'Avre before he went looking for snowcherries, but found a hungry Yeti instead.