there is an issue with command

my version says it is 1.20.31 but there is no space for it so i will say 1.12.30

I was playing with commads and found out this bug.

When I use "[,]" these characters, it seems to erase the commands behind.

I will attatchx  a video with it. You can see it happen from 00:18

It works like this even in the command block. 

 

p.s you might think it is working properly when you see the last scene but it works just the same again.