se/30 disk weirdness

I brought home an external FDHD for my SE/30 last night, to facilitate retrocomputing tasks. Plugged it in, switched on the Mac, tested it out, shut the Mac down, and unplugged the disk. Now, when the external drive is unplugged, the system somehow still thinks it's there. I get a disk icon with an "x" in it at boot as it tries to boot from this external drive which is not there and finds (surprise!) no system folder on the disk. The system then goes on to boot more-or-less normally from the internal SCSI disk. Once finder starts loading, I get a dialog box that (depending) says one of two things: "This disk cannot be read by this Macintosh. (Eject) (Initialize)" with the icon indicating the (non-present) external floppy. ~or~ "Initialization faild: disk is locked. (OK)" Dismissing these dialogs result in processing resuming normally for a second or two, and then another identical dialog being thrown up. Repeat ad infinitum, et ad nauseam. The internal disk drive continues to work normally (within the above constraints). As soon as I reconnect the external disk drive, everything is happy again. As soon as I disconnect it... bang. Nose demons. I am utterly baffled. What's wrong? How do I fix it? ok r.