Prior to mid-October 2016, image titles set in Shotwell were correctly exported to Piwigo. Furthermore, the checkbox in the export form "If a title is set and comment unset, use title as comment" did actually work. Neither of those features work anymore - it is as though the Shotwell titles are completely ignored.

As a check, I re-exported an album I had previously exported in October 2016 - the titles, which had worked OK last time, no longer worked.

I was using Piwigo 2.8.0, which had not been updated for roughly a year, so I believe the problem is due to a change in Shotwell version (apparently it got upgraded in November 2016) rather than a change in Piwigo. I have since tried upgrading Piwigo to 2.8.4, but that had no effect.

FIWI, I also checked the .jpg image files in Piwigo's upload directory and can confirm that the Title attribute is correctly set in the EXIF data but does not appear in the piwigo_images table - for images uploaded prior to October, the Shotwell title appeared in the "Name" column of that table.