"Reduce Screen Flickering" causes still fogs to lag?

[Daniel]

First, I had a fog that scrolled, an I noticed that when I checked the "Reduce Screen Flickering" box, the frame rate dropped about 3 frames. So I made the fog not scroll to see if it stopped the lag. The fog was completely still, and so what the player (I wasn't doing anything), yet the frame rate was the same as it was with the scrolling fog. However, if the "Reduce Screen Flickering" box is not checked, either way the frame rate is normal. So, does anyone know the reason why this happens? Is there any way to fix it?

 

[Dirtie]

All "Reduce Screen Flickering" should do is turn on Vsync which synchronizes the games frames with your monitor's refresh rate, therefore eliminating tearing. And yes, Vsync can sometimes cause a lower frame rate.