OK: for those who are able to do so, could I ask you to make a complete database backup and upload it to a suitable location (your own WordPress blog or hosting account, or else to Dropbox or a similar service) then share the link here as a private reply? As we’re unable to replicate locally this could give us a good chance of seeing the problem as it is in your individual installations.
Should anyone be able to go a step further and share before-and-after dumps – showing the database as it was prior to this problem surfacing/prior to updating then again after this took place – that would be particularly useful.
Thanks for your help and cooperation 🙂