I still cannot reproduce the problem of 9 differences. I have tried in Edge, Chrome, and Firefox on Windows 10. I will try on OSX in just a second.

The reason why it changes output after using square braces is because the tool is language aware. Before it could not guess at a programming language and so the input is text parsed into lines. After the language detection guesses this is JSON format and formally parses the input, beautifies it, and then compares the beautified output.

I already realize that if I am going to the trouble of parsing languages that it would be far more efficient to simply compare the parsed token lists instead of beautified text, but I haven't gotten there yet.