I did a clean installation of MiKTeX (latest version). Then I did a package update --- believe it or not, there were packages to update.
After the update, I tried running "Update Formats" from the settings... I started getting mesages that I needed to install file having to do with music tex: bagpipe something or other, and some other file having to do with music notation.
That is surely a bug, right? My sources are typeset correctly (so far), and they have nothing to do with music.