Basically, I discovered that on this post, only the first five links were becoming titles, and not the last two, but in the edit preview all seven links render as titles. I was going to report this as a bug in itself, but...

I discovered this documentation post which says that it's intentional that only the first five sites linked to will be converted into titles. If there are a lot of posts here that link to different sites as bare URLs, then I'll file an FR asking for that limit to be increased, and if not, I'll file a bug report asking for the preview to match the rendered post and only convert the first five sites.