Put the summary of the bug you're having here

What I expected to happen was...:
was that it would create a slime ship that would move around the sky.

What actually happened was...:
The slime block connected to the ship and piston created a graphical glich making the prismarine ship that i build start duplicating its own blocks and instead of breaking the redstone like it usualy did (i dont know how to make a slime ship) it just keept making more and more blocks.

Steps to Reproduce:
1. make a V that is 3 blocks long
2. line it with redstone
3. then in the middle under it put 1 redstone torch on each side on the wall of the V under it on the bottom
4. then put 2 pistons (one on each side und on the bottom on the wall like you put the torches) on the front of the V 1 block away from the torch that you put
5. put a slime block 1 block away from the piston you put erlier
6. put dark prismarine on the V in front one block behind the slme block inbetween the piston and the slimeblock but one block above
7. put one extra redstone ont he back of the V and then put a redstone on top
8. stand back and look
The attached file is the world the glitch is in