When the anvil is expected to destroy the test article (Pic 2), instead the anvil drops as item form and the test article remains intact. Bug also appers with dandelion (Pic 1, from a video by a Chinese player) and possibly other blocks.

Reproducing the bug

1. Place the test article.
2. Place a random block that is not affected by gravity (e.g. dirt).
3. Place as many anvils as you want above the random block.
4. Destroy the random block.