Well then it's a bug. It should stay floating but it doesn't. If placing stuff floating is supposed to be a feature of setblock, it should work for all blocks.
If this is intended, why doesn't it work for redstone wire and redstone torch? EDIT: I created an issue about wire and torches: https://bugs.mojang.com/browse/MC-63698
Well then it's a bug. It should stay floating but it doesn't. If placing stuff floating is supposed to be a feature of setblock, it should work for all blocks.