• 1. Place a command block and copy in this command (or just not a setblock command):

     /setblock ~ 257 ~ command_block
     

  2. Power the command block, it should have now an error message ("... is too big, it must be at most 256") in the previous output line
  3. Change the command to:

     /setblock ~ ~ ~ command_block
     

     Amd power it again

  4. Look again at the previous output line

It has still the error message like before

This is a double bug as

• The success output is missing
• There is still a last output even no command was performed at this command block (that's probably not intended like other NBT tags like the command itself was reset