Test behaviour different to Calibre behaviour

I wrote a regex to extract series_index, title and author and tested the functionality. It extracted the title, author and series_index as expected. I didn't include a series as I just wanted the index to show the sequence of the books by the author.

When I actually ran the "Add Books" Calibre extracted the title and author but NOT the series_index.

I have attached jpg's to show this.

Is this behaviour to be expected? Calibre doesn't like a series_index without a series?

Attached Thumbnails