They can't dance either way and this improves their pathfinding behavior as well as their visual movement
left side current svn, right side this patch;
Turn rates were floored to 4 in D4163 to mitigate the useless turning and twisting of large units trying to pathfind.
(See the gif on D4163)
But with the InstantTurnAngle disabled, I can't reproduce that bug (or at least not very easily):