Carousel/slideshow/ tiled galleries mystery

I am able to create jetpack carousels and slide shows from the media library.

However, it appears that I cannot create a post, upload images to it, and then create a slideshow or carousel from a gallery created with files uploaded to that post.

Here’s what happened. I was going to try the carousel for the first time, but to test it, I created a test post, then made a gallery from images uploaded to other posts. The carousel worked great.

I then created a new post, uploaded images to it, created a gallery from some of those images, and I couldn’t get the carousel to load. Moreover, when I clicked an image from the gallery, it showed _all_ the images uploaded to the post, not just the ones from the gallery.

Next, I created a new post, then made a gallery from the images uploaded to the previous post and — hey, presto! — the carousel worked.

Is this a bug? Am I doing something wrong?