Disappeared blocks

Disappeared Blocks

I don't actually understand why it happend

Yesterday I started making one mechanism in 14w26b, today I have updated to 14w26c and the command blocks, redstone, quartz, wool, clay, half slabs, basically all blocks, that are not stone disappeared.If I will open that world in 14w26b again, missed blocks will appeare, but without NBT (No command in Command Block, no text in signs)