I am still having the issue, however, I have found out more information:
This bug commonly happens when I type text in a command block that is being powered by redstone at the same time I am typing the text.
I have also found out a way to fix this bug: If you just break the command block and place it again, it works. However, it is still really annoying and needs to be fixed. I HAVE reproduced this bug on another computer, so I think this should be reopened. They were both Apple laptops.
I am sorry, I forgot to mention that this only happens in command blocks. Typing/copying it into chat works fine. I have tested that, and I got what you got. I find it strange the EXACT same command works in chat but not command blocks.
Ok, I will post some screenshots later today. Oh, and if invisible control characters ARE being added, how do I remove them?
Thank you for your help.
That's really strange. Maybe the world is corrupted.