You can no longer place blocks at y=255, and the error message doesn't display.
To reproduce:
In an older version, create a pillar of blocks all the way up to the world height. When looking at the topmost block, it should say 255 for the y.
Load that world in the current snapshot.
Note that when you try to place a block onto the topmost block, it gives the error message.
Break the topmost block.
Try to place the block again. This will not work and no error message will be shown.
Comments 2
It is strange that you can place torches, banners etc in the topmost space, but not other blocks, but that's understandable. I do however think that if you are going to be prevented from placing full blocks there, then there should be a message, rather than only if you try to place it actually above the limit
Cannot Reproduce / Works As Intended
You can't manually place blocks at 255 for a while now (1.7.10: not possible), and that is intentionally.