The bug

When you bonemeal a small dripleaf plant to grow it into a big dripleaf plant, blocks above it are destroyed. Even blocks that are supposed to be unbreakable, such as bedrock, command blocks, and end portal frames can be destroyed. This does not occur when bonemealing big dripleaf plants.

To reproduce

1. Place clay 3 blocks beneath an unbreakable block.
2. Place a small dripleaf on the clay.
3. Bonemeal the small dripleaf.
4. If the small dripleaf grew too short to destroy the block, then break the newly grown big dripleaf and go back to step 2.
5. Observe that the unbreakable block was destroyed.

Video

Small dripleaves break unbreakable blocks.mp4

Credit

This was discovered by Real_Media1501 in this reddit post.