In all prior versions, the variant of breakNaturally without an item passed in was expected to drop whatever items should drop when using the ideal tool for the block. As of this commit, https://hub.spigotmc.org/stash/projects/SPIGOT/repos/craftbukkit/commits/46a138606655ce6a79e62c63a0d27e10643975ea#src/main/java/org/bukkit/craftbukkit/block/CraftBlock.java, this is no longer the case. Block#breakNaturally() now breaks the block as if broken by the a hand, rather than dropping the ideal drops of the block.