Drawbridges can "place" blocks down into the void and above build height. The blocks are not actually placed, and you can't get them back. Tested with an extended drawbridge.

To reproduce:
Get a drawbridge
Place it pointing up on y=255/256
Put in a stack of blocks
Activate the drawbridge
Open the GUI and watch blocks get used up without being placed
Deactivate and expect the blocks to come back (Spoiler: they won't)