'Add Media' causes post to link to attachment page (Bug?)

I wrote a post today, the first in 4.0 on this site and had issues.

I wrote a post, then uploaded a zip file using the “add Media” button in the post editor dashboard. The URL of the zipfile I pasted into a metabox to create a styled download link as was my past behavior.

I did not insert the media in the post.

On preview, all was well. On publish, the post url points to the attachment page of the zipfile instead of the post.

I disabled all plugins, no joy.

Success when I deleted the post, re-posted then copied the link into the metabox from the media library rather than using the ‘add media’ button.

New default behavior, or was I in the past using an undocumented featured that no longer exists? ??

Cheers,