So I noticed the slipperiness value when creating a block and wanted to test what would happen if I put it to 0 (default is 0.6)
When I made the block and tried to walk on it, the player started sinking through the block and after a second it shut down the internal server and said Connection lost for "Invalid move player packet received" and put me in the server list (even though I was in solo). When I got back in the world it kicked me again after a second but I managed to get out by flying in creative on the third time. Next, when I put soulsand on top of the block to test it (soulsand isn't a full block so it takes the slipperiness from the block below it) and walked on the soulsand it started sinking again but instead of shutting down the internal server it froze the game completely and I had to close it.
Walking on a block with slipperiness value of 0 makes you sink through it for a second and kicks you out of the solo or multiplayer world;
Putting soulsand on the same block and walking on the soulsand makes you sink through it for a second and crashes the game with exit code -805306369