When trying out the new render distances of minecraft i noticed that i get a lot of flashy chunks which will stay this way nomatter what you do. Increasing the distance will cause more of these chunks to appear.
I captured the issue on video: http://youtu.be/OmLZ07OyqYc
Setting it to 12 chunks seems fine, everything above starts spazzing out.
Restart your client with the new render distance and it will work fine.