Thanks you for your prompt reply. I had restarted the Mac and it didn't seem to work. However, now it is working and I think I understand where the problem is. This is a bit complicated, but let me explain as concisely as I can.
Firstly, the "Download 1 item" box is still showing and there doesn't seem to be a way of getting rid of it. A reboot will no doubt fix that problem.
Secondly, I did notice (I probably spend too much time looking at Activity Monitor, but in this case maybe it was useful) that there was, in the network activity window, data received for a few seconds after I clicked Install in the original message, the one saying that I needed some software after I plugged in my iDevice. Was that the needed software? I suppose it was.
Thirdly, in exploring (today) whether the syncing was indeed working, I experimented a bit more with Music in the Finder window for the iDevice. I sync selected music and I choose the playlists that I want to sync. The two albums that did not sync before were new albums for existing artists that I am syncing. When I looked at these artists, the new albums were checked, i.e., sync these, so I thought they'd be synced, but they were not. When I deselected these artists and selected them again, the sync worked. So the problem, then, is that Music on the Mac, when I add albums to the library and create a playlist for them I suppose, is automatically indicating that the new albums for existing synced artists are to be synced, i.e., they are selected, but really they not selected, they just show as selected. So I think the bug is in Music on the Mac. Thanks for listening. I hope I have described this accurately.
