The bug

If you die after you lost a home respawn anchor, blocks behave extremely weird.
So if you place a block, destroy it, place a different block in the same place, the new block is replaced with the old block.

Steps to reproduce

1. Place a respawn anchor
2. Power it up with glowstone
3. Set your spawn with it
4. Destroy it
5. Die
6. Respawn
7. Place a block
8. Destroy it
9. Place another block at the same location
   → The old block reappears again