Water Incorrectly freezing above level 90

It appears that there is a bug with the way water freezes into Ice above level 90 in the latest snapshot? First, I realize that this is supposed to happen, however, I would expect ALL water sourceblocks that are exposed to sky to freeze if not near a light source (such as glowstone, redstone lamps, lava or torches) However, I have a 9x1 pool of still water source blocks that I am moving via pistons, and only 2 of the blocks are freezing, while the rest stay liquid? This is occurring in an extreme hills biome. I have double checked and I have no light/heat sources anywhere near the water, and the water itself is placed at block level 95. I didn't see this reported anywhere, so I hope I'm not wasting anyone's time! Please see the attached screenshot, I have moved about 60 blocks of ice, and only these 2 seem to freeze. Thanks for an amazing game (zero sarcasm there!)!