UPDATE: Problem Solved!
I noticed the toolbar icon for a floppy disk ("Daddy, what's a floppy disk?") at the very left, which said "Save" when I hovered over it.
Changed a tag and clicked that icon.
Popup appeared, saying "Saved tag in 1 of 1 files."
It was updated.
Tried editing the titles of two tracks, one after the other, and then hit Save.
Only the second track was updated - moving from one to to the next, the change to the first was not saved.
I prefer the older behavior, where moving from one track to the next saves the change to the track just left, so I went exploring in File>Options and found, under File>Options>Tags, the first checkbox, "Save tags when using arrow keys/single mouse click."
That was unchecked, so I checked it. (When was this default changed?)
Tag editing behavior back the way I'm used to.
Now my only, much less important, gripe is that as I use an alphabetcal heirarchy of folders for my music, I set the root of my heirarchy, which has four subfolders (A-G, H-M, N-S, and T-Z), as my starting folder.
On startup, the program used to show those four folders when I hit the Change Directory button, so I could then navigate to where I want to go.
I set it the same way as always, but hitting Change Directory now comes up at the top of my Desktop heirarchy, like Explorer, so setting a starting directory does nothing more than show that folder as highlighted when I scroll down to it. (Checking "subdirectories" on that page makes the program display all tracks in the whole heirarchy on start-up, which is horrible.)
I also liked the fact that once I had chosen an artist's folder and one of that artist's albums, hitting Change directory brought up the list where I already was, so I could go up one level and see the other albums by that artist. Now it always takes me back to the root of the Desktop heirarchy.
How do I restore those older behaviors?
PS Should I make this question a new thread?