Can you post a screenshot? I've never seen or heard about that happening. It's certainly not a "feature"...
I've seen it... a lot. I don't use the internal editor to edit, I use Visual Studio Code and just paste into the internal editor.
Here is a screen shot showing the marks (blue). One of those marks is made each time I click in the script in the internal editor. I am looking for a way to turn that off.
I'm never seen anything like it before... Maybe it's a Mac issue.
It's a bug. You can't turn it off. I recommend using an external editor like Visual Studio Code.