– Kinda a long story –

So, I was making a concept for a minigame where the player has to constantly keep right clicking the dragon egg to get points.
It used the following system:

1. Player right clicks egg
2. Egg teleports by game mechanics and converts into a FallingSand entity.
3. A command block clock runs and assigns a scoreboard value to this entity.
4. Another command block kills the entity with this scoreboard value.
5. – Other stuff happens that has nothing to do with dragon egg –

And everything seems to work perfectly. No phantom blocks, no phantom entities.

Until you relog. Every place the egg was killed has turned into a dragon egg block!

Also, the eggs are proper blocks. If you block update them, they fall to the ground as they should.

– Steps to reproduce –
1. Set up a command block fill clock:
a. Put 3 command blocks on top of each other with a one block gap in between each.
b. Enter the following commands:
Bottom: /fill ~20 ~1 ~20 ~ ~1 ~ stone 0 replace redstone_block
Middle: /fill ~20 ~-1 ~20 ~ ~-1 ~ redstone_block 0 replace stone
Top: /setblock ~ ~-3 ~ redstone_block
2. Put a redstone block on top of the top command block.
3. Place another command block adjacent to the bottom one.
4. Place a stone block on top of it. (If it doesn't turn into a redstone block, you need to move it in a different direction)
5. In the command block, put in the command /kill @e[type=FallingSand]
6. Place down a few dragon eggs then right click them.
7. They dissappear like they should.
8. Relog: There will be mysterious eggs floating.

See the screenshots for more info.

Thanks!