Custom Groups in Companion CC (Dewey)

In Calibre in the “Subject” field I have classified my books using Dewey. Thus on the Left Hand Side in Calibre, as well as the usual “Author … Series … Publisher..” I have “Subject” which provides a hierarchical structure (see picture). E.g.
300Anthropology
500NaturalScience
...... 500NaturalScience.510Maths
.............500NaturalScience.510Maths.512Algebra

This provides “automatic” subject filtering in Calibre. I am trying to do the same in CC. The “OTB” CC gives me automatic Title, Author, Series (etc) Grouping. I added “#Subject” expecting the same to happen, but it seems to be treated very differently. I :
1. Click on “Group By #Subject” (expecting to see them grouped by …. Subject),
2. It prompts me to enter a search term.
3. I enter “512” (i.e. Algebra)
4. It tells me how many are in that “Group” but doesn’t display the list.
5. I THEN need to “Ungroup” them to display the list of books
6. I can then “Group By” (Author, Publisher etc)
So instead of a ONE click action, it is now a six click process. It seems that the user custom “Group”, functions more as a “Filter” rather than a Group. Is that correct ? How can I get it to behave as an actual “Group” ?

If I can’t “Custom Group”, then it would seem that I would need to copy the Subject to the Tag Field then use the Tags or some other way. Any thoughts ?

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