I don't know what the fix is as I don't know what is at fault. I did not change my tvheadend version when updating Kodi to Jarvis so something has changed either in Kodi or in the tvheadend plugin.
If I edit the log files for all the recordings and clear the "subtitle" entry then everything displays fine in Kodi. The subtitle information however is then missing in the tvheadend web gui and there is no "description" column I can add in its place. Besides I don't want to have to edit log files post-recording just to get them showing properly in Kodi.
So where does the issue lie exactly? It was working OK and now it isn't so either the Jarvis update or the accompanying tvheadend plugin has been changed create this issue.
Should a request go in for tvheadend be modified to not write the description text to the synopsis (and then have a description column added to the tvh gui) or do we need to get whatever workaround was in previous versions of Kodi or the tvh addon reinstated?