See this question:
Are (non-void) self-closing tags valid in HTML5?
Basically, HTML5 doesn’t really do self-closing tags. Instead it has void tags, like <br>. This also explains why <script> isn’t self closing when you are using an external js file; <script> isn’t a void element. The SVG you are writing is actually html, so it has to follow HTML5’s rules, not XML’s.
I think you should just add a closing tag so that you can get the benefits of more important warning/errors in the console. Alternatively if your page was XHTML, I believe you could use a self closing circle tag.