When using the command /spreadplayers to disperse, players are dispersed to kelp and seaweed near the surface of the water. It is expected that this would not be possible as players cannot be spread onto normal water blocks.

Steps to reproduce:

• Run the following commands on a superflat with void preset

  /fill 10 -62 6 6 -62 10 minecraft:stone
  /fill 10 -61 6 6 -61 10 minecraft:seagrass

• Run the spreadplayers command

  /spreadplayers 8 8 0 2 false @p

• Observe that you will spawn atop the sea grass.
• Replace the seagrass with water and use the spreadplayers command again

  /fill 10 -61 6 6 -61 10 minecraft:water

• Observe that the command doesn't work (intended behaviour)