In what appears to be some new integration between Facebook and the Facebook-owned Instagram, it looks like Facebook is now including Instagram likes in the total like counts on Instagram photos posted to Facebook.
The like totals look the same on Facebook. For instance, for the photo below, Facebook says that 9 people like the photo (me, three of my friends, and 5 other people)...
But when I click further to see who likes the photo, 2 of those 9 likes are actually Instagram likes. In reality, only 7 of those likes happened on Facebook. The other two happened on Instagram, and Facebook is including those in the like total. Facebook tells you this, and allows you to click a link to the photo on Instagram.
What's interesting is that the photo above was not cross posted from Instagram. It's an Instagram photo that the user manually posted to Facebook after taking it on Instagram.
I've reached out to Facebook and will let you know when I hear back.