Okay, I ran through my procedure again. Every time I try it, it seems to go differently, which goes against every ounce of common sense in my engineering brain. This time, during the install, I got some strange "cannot remove /usr/share directory - not empty" errors, followed by some "out of space" errors (even though I had plenty of space in my root partition. This stopped the install, and an "apt-get -f install" instructed me to run "dpkg --configure -a", at which point it then resumed.