Command blocks are unable to run the /backup command, the following error is given:

"You do not have permission to use this command"

Attempting to use execute like so:

execute @p ~ ~ ~ backup

produces:

"Failed to execute 'backup' as edwardg"

Running the command normally though chat works as intended. Not sure why a command block is having trouble.

This because I set the permission level for the /backup command to 3, I'm going to change it back to 2 in the next update.

Fixed in 1.4.