I can build 257 blocks high, build 256 blocks and place water and lava.
Linked issues
Comments 2
@Synchunk
Why is this valid? Not only has is been fixed, but it's also a duplicate of MC-39120.
MC-80004
Water and lava placeable on top of level 256
Resolved
Duplicate
0
This bug was actually fixed back in 1.8.2. Also, you got your numbers wrong, 255 is the layer you could only build certain blocks on.