I built up to y=255 in creative mode in a 1.8 pre3 world.

I tried to place another block on top but it never places.

I can use a piston to push a block into y=256 and when I try to place a block on top I get the expected message of "Height limit for building is 256 blocks"

But I get no message at y=255, the block just fails to place.

Is this by design?

Update: I can place a layer of snow just fine on top of a y=255 block, put when I try to put another layer of snow on top of that I get the message "Height limit for building is 256 blocks"