I'm now facing another problem, I can't seem to be able to change the grouping order (year) from ascending to descending..
Grouping order sorting is only alpha-numeric.
That is, it only sorts ascending.
Testing this now, this isn't strictly true.
If your first 'Sort By' selection item and 'Group By' selection match, then you can use the "Sort Ascending' or 'Sort Descending' options at the bottom of the first 'Sort By' right-click option.
This isn't always true either.
I've just spent over an hour looking at this and I can't find any way to explain how sorting is applied to groups and albums.
Some examples:
Group by: Artist - Sort by: Artist / Album
Group by: Genre - Sort by: Genre / Album
Group by: Decade - Sort by: Year / Album
Sort by ascending/descending: Affects order of groups, then albums.
Suggests the sorting of all albums is done first, then split into groups as the first sort tag changes.
Group by: Artist - Sort by: Year / Album
Group by: Decade - Sort by: Decade / Year
Sort by ascending/descending: Affects order of albums only, groups are always ascending.
Suggests the grouping is applied first, then sorting is done within each group.
If I had to guess, I'd say it's a combination of things like whether the grouping tag is alphabetic or numeric; whether the tag is a string, number or date; whether the sort tag matches the grouping tag; with some extra sorting hard-coded in for some common tags like Artist.
Then you also have to consider that custom sorting sets have their own sort order for each tag, and how the
Sort Ascending / Descending options on the menu should affect those, if at all.
Bee excellent to each other...