When you place a command block minecart and put a command in it, the exit out of the command block minecart and open the UI again, you will notice that the command you just entered is gone (the tick delay will also be reset). It will still work, even if you reopen it. This can get really annoying when trying to edit commands inside of them, as you have to retype anything that you entered into it.

Steps to reproduce:

• Use this command to get a command block minecart:

  /give @s command_block_minecart

• Place the minecart on a rail, and then put any command into it.
• Exit out of the command block minecart, then activate it using a powered activator rail. It should work.
• Now, open the command block minecart up again. Notice how the command you entered is now gone.

What should happen:

• The command shouldn't be erased from the command block minecart, and same with the tick delay.