I attempted to break several blocks, including Oak Logs and Obsidian, and frequently there would be a block breaking sound followed by the status of the block going back to its original unbroken status and dropping no item. the action of breaking the block still took damage to the tool used to mine the block, and it would generally be able to be broken at a second attempt to mine the block, as well as drop the intended item.

Notes

• Was using unenchanted diamond pickaxe at the time
• Was attempting to break Oak Log and Obsidian blocks
• Most of the obsidian blocks this was attempted by had been lava blocks put out by a water bucket