Wow, okay… I am at a loss.
I am still trying to figure this out, but I wanted to respond so you won’t think I’ve overlooked or forgotten your issue.
I’ll look into that StackOverflow page, but my initial reaction is that it has to be something unique to your server or configuration.
After all, you can see all of the icons when you visit the demo pages, yes?
Please post your Software Environment info (Admin Panel > Settings > Theme) or send it to me in a private message.