Diamonds spawning at level 70

Hello. I was playing with my friend on a vanilla minecraft server on my Machintosh when my friend noticed that there were diamond ore patches (only a few) scattered in a forest biome near the sandy coastline at around y=70. The problem is 1) that terrain was generated in 14w28b, loaded in 14w28b, but then when we saw it in 14w29b there were patches of diamonds, 2) diamonds do not spawn at y=70! They spawn at y=16 and below! We destroyed these blocks and did not take advantage of the bug.

Thank you.