This is a very minor bug. Very minor. Most users won’t notice or worry about this.
I noticed because I’m building a calculator and I wanted to display the result in a basic text field. So, I wanted it to show 0 (zero) until the calculation had been done. I can insert a basic text (I noticed the same problem with heading, but not rich text) and put 0 (zero) as the content, but it won’t show on the front end. If I put 1, a, or any other single letter or number, it does show fine. It just doesn’t work with zero!
Again, it’s a super minor issue, but I wanted the output of my JS calculator to show 0 until the calculation has been made. I did end up using a different way to show the 0 before the calculation has been made, but this is still a bug (very minor) I think!