If you try to break a block that is protected by the spawn protection on a server, but interupt the breaking before the block breaks, you get a warning in the console:
[15:45:39] [Server thread/WARN]: Mismatch in destroy block pos: fk

fk

How to reproduce:
1. Start a server with spawn protection enabled and join.
2. Begin to break a block like grass.
3. Stop breaking the block.
4. See the warning in the console.