Place a Sponge Down Twice (One ontop of another) Place an Anvil beside it; watch it fall then place a different block where you placed the anvil originally and it puts an anvil there instead and the anvil fails to hit the ground.
This happens in a world that has the height limits set from -1024 to 1023 (When testing on a fresh world I could not reproduce the issue)
The same thing happens for any Falling Block type when placed next to the Sponge.
NOTE: I could not reproduce this on a SOLO world, perhaps this only effects Servers. Will re-post more information if/when I have time to investigate further.
Please provide some screenshots or videos of this issue occurring whilst the F3 debug screen is enabled.