Thanks for the notes.
With 2015 turned on, it works. It’s not a plugin.
But here’s the weird thing: this site is a set of sites all using the same theme. None of the others have the problem.
It’s a custom theme I designed based on Automatic’s Underscores. I haven’t done anything weird. I’m not calling in stuff outside of what Automatic is calling in. If I go to a site that is working, and take their theme and replace this one completely, it still has the problem. So I’m really scratching my head as to what the difference is.