gvim doesn't refresh screen correctly on windows when scrolling

Hi,

I use gvim7.4 on windows7. When I scroll using mouse wheel, the text can't be displayed correctly sometimes. You can look at the picture attached. The red arrows are added by me to indicate that the "e", ":", and ";" are drawn twice. Gvim7.3 also has the problem. I guess the reason is that gvim doesn't refresh screen correctly on windows when scrolling.

Is anyone else has the same problem? How could I solve this?

 

Thank you!