I'm encountering a specific instance of mouse lag when the following actions are taken:

• Open NPC dialog box for *any* NPC who can open a store interface
  
• Browse store items, exit store interface back to NPC dialog box

At this point I experience serious mouse lag which makes the mouse pointer very hard to control and it stutters around the screen, overshooting the dialog box choices with normal mouse movements. Once I carefully steer my pointer back into the dialog box using tiny, deliberate mouse motions and click the choice to close the dialog box, the mouse resumes normal speed action - no lag.

Other interactions with "non-shopowner" NPCs' dialog have no lag. No mouse lag experienced with "shopowner" NPCs' regular dialog choices as long as I don't open the store interface.

Very odd and specific to a certain series of actions. It's certainly not a game breaker, but it's annoying. Apologies if this has been brought up already. I couldn't find it anywhere.

Otherwise, I have a pretty robust system that has been running the game easily on maxed settings with no issues: i7-920; 6GB RAM; GTX 260 3x SLI; etc.