Got it. You made me look farther into what I was doing. I was sorting in the table view (by clicking on the column heading) and then switching over to the thumbnails view. That order didn't carry over. I also didn't quite tell the whole story -- I like to sort on title within composer. In the table view, I can do this by sorting on the title heading first, and then on the composer. But, as noted, it doesn't carry over to the thumbnails view -- just the composer order carries over (titles aren't necessarily sorted).

HOWEVER, if I set up a custom sort using that option under the sort selection on the view dropdown menu, to do a composer then title sort, it will work. Then both the table and thumbnail view appear as desired.

I also notice if that one then clicks on the column heads in the table view to sort in a different order, that sort takes precedence over (and indeed replaces) the custom sort order. Whatever way you sorted last, by whichever method you choose, is what is in effect.