User IDs show as comment authors in Plone 4.x after migration from plone.app.discussion
If you’ve migrated your site from earlier versions of Plone to the latest ones in the 4.x series, or else have started using plone.app.discussion earlier than that, you might have come across a situation where comments on your site show user IDs as authors rather than a user’s full name. If you see this anywhere, chances are your comment’s migration didn’t go according to plan, and that the Creator information didn’t get recorded correctly on the comment.
I’ve just written this on the Collective developer docs: http://readthedocs.org/docs/collective-docs …