If you have a block in inventory with datavalue 1 (/give @p iron_block 1 1), it will be flat.
And if you place a block (/setblock ~ ~ ~ iron_block 1), it will be pink and black!
MC-50473
Block Bugs (In inventory, and in World!)
Resolved
Duplicate
0
This seems to be happening with any block with a data value >= 1 that isn't like wool or stained glass.