The double-download problem is intermittent. Also the number of get requests varies.I don't know. I think, theres no double-download, the browser downloads parts (can see in browser network analysis) (it's the filesize of your song 2M?)
stackoverflow don't help really
the multiple requests have status 206 (partial content load)
update: yes, you make a mistake in the editing (changing the play button is not nessary)