I’m having the same problem, the issue seems to be that -
When using right click to control turning, the location of the mouse passes over npcs/players the turn action is interrupted/slows. The more NPC’s/Players around the more this happens.
This bug is extremely irritating and only appeared for me after my return from holiday on 28/09/12, prior to 14/09/12 it was fine, so this bug has appeared during a patch in that time for me.
I will also submit this post as a bug report.