Brief Description:

Anvils are deleted upon landing at the same time on the same block.

Steps to Reproduce:

1. Place several anvils above a cobweb.
2. Make the anvils fall and stack inside of the cobweb.
3. Destroy the cobweb.
4. You will notice once the anvils hit the ground, that you receive the incorrect number of anvils back.
(See attachment below).
Observed Results:

You only receive a small portion of the anvils you placed.

Expected Results:

You should should all anvils that you placed.

Screenshots/Videos:

I've attached a video which showcases this bug in action. Here you can see that I place 5 anvils 1 block above a cobweb. I then made them fall and stack inside of one another by destroying the block placed below them. I then destroyed the cobweb and upon the anvils landing, you receive the incorrect amount of them back.

Notes:

This bug does not seem to occur with any other blocks that have gravity other than anvils.