The emerge log for sys-fs/udev-189 wrote: "This version of udev moves the files that were installed in /lib/udev to /usr/lib/udev. We include a backward compatibility patch for gentoo to allow the rules in /lib/udev/rules.d to be read. However, bugs should be filed against packages that are installing files in /lib/udev so they can be fixed." app-misc/media-player-info-17 installs files into that old location, so it should be fixed. Remerging the package is not enough to fix this issue.
Looks correct to me: >>> /usr/lib/udev/rules.d/40-usb-media-players.rules >>> app-misc/media-player-info-17 merged.
It appears I was copying this one from the wrong terminal window, and a rebuild did indeed fix this one. Sorry for the noise.