New-post emails suddently not clipped by the “more” tag

For ages, our blog has had emails for each new post go out to subscribers. There is an intro of text in this email, only the part of the post before the “more” tag. This subscriber email is handled by wordpress.com.

Just a few days ago however, all new-post emails have the whole text, as if there were no “more” tag in the post. There hasn’t been any new plugin or other update to the site that I know about.

Is anyone else seeing this? Any idea how I can diagnose it?