Thank you so much for sharing this here! I'm having an issue, and I'm not sure if it's an issue with squarespace or sharethis.
I went to sharethis and put the code in my Blog Post Code Injector... I didn't like how it showed up on the page initially, so I went and adjusted the customization, pasting in the new code. (I am trying to get the share buttons to show at the bottom of the blog posts.)
Now, they've disappeared, and I can't get them to reappear at all. There was a message about needing to verify that the js has been placed in the <header>. I cleared cookies, redid it all, and finally got a "Verified" message. Code in header, and code in blog post code injector.
Nothing is showing up on the page. Does it take time to actually show up on the blog post on the website? I'm not sure if I've done something wrong.