That didn't help. However, adding a "blacklist=floppy" option to kernel boot did the trick. I think "floppy" is included in the initrd image and is loaded by the kernel in the early phases of boot; I also suspect this happens because I let the Debian installer load "floppy" when I set up my system.
That is (somewhat) correct; the scripts which create the initrd image will normally (in the default install) put all framebuffer, acpi, filesystem, and hard disk drivers into the image. Have a look in /etc/initramfs-tools/initramfs.conf to get some idea what goes on. I had problems a few months ago when I changed my kernel and discovered that the scripts included (but didn't load) the 'md' driver.