Spreadplayers often sets the entity/player at y=255

Version: 1.2.0

Summary:
When using the spreadplayers command, players will often be spread to the maximum Y co-ordinate instead of being spread to the highest point of a X, Z co-ordinate. The effect seems amplified when using a larger max range.

Impact:
Severely game-breaking for any maps which use spreadplayers to randomise player or entity positions!

Repro Steps:
1. Create a new world
2. Use the command /spreadplayers 0 0 1 20 @p
3. You will be spread between 1 and 20 blocks around the 0,0 co-ordinate. You should notice that your Y co-ordinate is 255 instead of on the ground. If you are not at 255, then the command ran properly. Repeat step 2 until you are put into the air at 255.

Observed results:
Most of the time the player is teleported to the max build height, which will obviously result in death if the player is in survival or adventure mode.

Expected results:
The player or entity should be on the ground after using the spreadplayer command.

Screenshots/videos attached:
No