If you try to use setblock to place a block with no set damage value, and it does not have a damage value 0, it does not place the block and instead gives an unknown error.

An example:

/setblock ~ ~ ~ minecraft:furnace

Produces an unknown error, instead of defaulting to:

/setblock ~ ~ ~ minecraft:furnace 3

In the previous snapshot, the command would place a furnace with a proper data value, instead of giving the error