[Plugin: podPress] item specific tags itunes:subtitle not updating

I am using podPress v.8.8.10.17.
My podcast URL is http://www.vantagepointchurch.org.au/category/podcasts
The RSS feed generated by podPress is http://www.vantagepointchurch.org.au/category/podcasts/feed and finally the iTunes Store URL for my podcast is https://itunes.apple.com/au/podcast/vantage-point-church-podcasts/id749691893

I have been trying to set item specific iTunes:subtitle tags so that they show in the description column of the its page. I have tried by setting them to copy the post excerpt and I have tried by setting a custom value.

When I try using the excerpt, the RSS feed takes the excerpt value and adds a value such as “this post first appeared at …” into description tags. The description column on the ITS page shows nothing. This the things are currently set.

When I use a custom value, the RSS feed acts as if there were no value at all and takes the content of the post and places that into description tags. The ITS page ALS shows nothing.

Could you help?