On my world that I had just updated to 1.8, I saw some random 1.8 blocks in place of 1.7 blocks. I did not place them because I just updated the world. Plus I found these blocks in chunks that were loaded in 1.7(See Photos)

While looking around some more, I noticed some water blocks had dissapeared. (See Photos)

Thes weird things were only happening in already loaded ocean.