There should be an option on the in-game bug report for living story content bugs. At the moment the nearest option is ‘personal story’, but the subheadings are not always relevant.
The older living story chapters will probably be played less often and bugs might occur with future updates. Having a clear way to report them will hopefully help Anet fix them faster. Quicker fixes mean happier players…especially if people are paying in gems (and therefore real money) to buy past living story content.