Huge Pieces of grass disappeared after updating to 1.8. leaving black shadows on it's place, which disappear when i am standing in them. .

It only affects the grass block layer. .. btw. a friend of me has the same Problem. But only in really old generated Worlds. Newer Worlds are not affected.

After downgrading the Grass is back again.
(offtopic: but instead my items gone.. i read it in the FAQ later that downgrading is frobiden,... a warning in the Update would have been nice. Because we are quite used to downgrading)

Attachment, Picture bevore and after update: