When any block affected by gravity tries to land on a space at Y-level 0, it breaks as if it fell on a torch instead of solidifying normally.  The block the falling sand entity tries to land on doesn't matter as long as it is located at Y-level -1.

I have tested this using gravel, sand, and an anvil.  All three trigger the bug, and the anvil makes a breaking sound, but does not take any damage in the process.

Steps to reproduce:

1) Place a solid block at Y-level -1 for the gravity-related block to land on.

2) Place the gravity block at Y-level 1.  After some testing, I have noticed that I can only reproduce this bug if the block falls down 1 space.

3) When landing at Y=0, it should break as an item instead of properly placing itself.