On a collaboration system in which the post template does not contain a synopsis form (for example this one), a synopsis is auto-generated in the Post.pm code: getSynopsisAndContent.  This can be displayed in the collaboration template.  However, if someone edits the post (for example changing a detail in the first sentence), the synopsis is NOT re-generated.  The code's logic says only generate a synopsis if synopsis is empty -- which it isn't on edit, since it was generated by the first post.

The tricky thing here is to distinguish between an auto-generated synopsis (which should be re-generated on edit) and a user provided synopsis which should not be touched.