When setting a command block to air using /setblock, it outputs "The block couldn't be placed", even though the block does actually get removed. However, it does not cause a block update. Note that it does work correctly with /fill, and that only the combination command block and air currently does this. Replacing the command block with another block works correctly. The console also shows nothing unusual when doing this.

Steps to reproduce:
1. Place down a command block
2.

/setblock x y z air