Well, I now think that this is a "feature," much in the same way that the smartphone integration is a "feature." My best guess as to what's happening is that the whatever music you upload to the HDD is compared to the onboard Gracenote DB, looking at folder/file names. I even tried stripping all tags...still ended up playing alphabetically. I tried prepending the songs with letters instead of numbers...still ends up playing by title. One thing I haven't tried yet but would conclusively prove the point, I think, would be to upload an album with all tags stripped and fake folder/file names. I'll give that a shot once I can convince my third son to go to sleep....

Just to be clear, this is using the Music Collection search feature. I can drill down by selecting the actual upload (USB1, for example) and going to the album through the hierarchical file structure -- then it will play the songs according to the unaltered file name order. In an ideal world, the system would take whatever you upload to the hard drive and use your filenames first, tags second (if that's even possible), and the built-in Gracenote DB last -- and get rid of the clunky file folder structure that's really not necessary.