Fill Command is being Censored with #

After typing in a regular fill command into a command block (impulse, chain or repeat) it will sometimes replace all of the text inside the command block with ####### making the command block completely useless, this only seems to affect new command blocks, not preexisting ones and it seems to happen about 90% of the time, please look into the issue and provide a fix at your earliest connivence, as a map builder and a event organizer this is extremely frustrating for me and my team to have to deal with and work around this issue