The drawbridge will not accept some blocks in it's placement slot, such as Seared Tanks, and other drawbridges. This is due to adding them to the blacklist by default. The OP of the forums thread says you can put drawbridges in other drawbridges, and I would like to. However, I can't figure out how to allow them.

Intended behaviour to avoid duplication of items, similar to 1.6.4 default blacklist.
Corrected the forum OP regarding using drawbridges in drawbridges.

Would it be possible to make certain blocks placed by the drawbridges not have tile drops enabled, like the gamerule?