sane is driving me insane ("ignoring libusb devices")

[Anne Bennett <anne%porcupine.montreal.qc.ca@localhost>]

I can't get "sane" (sane-backends-1.0.20nb3 from pkgsrc, on 
NetBSD-50.1) to see my scanner (HP PSC 1500).  The kernel
sees it as a printer (which it is, of course):

  ulpt0 at uhub2 port 1 configuration 1 interface 1
  ulpt0: HP PSC 1500 series, rev 2.00/1.00, addr 2, iclass 7/1
  ulpt0: using bi-directional mode

but sane-find-scanner doesn't find it, even as root, either
without a path specified (using "-v", showing relevant lines):

  checking /dev/uscanner... failed to open (Invalid argument)
  [ditto for /dev/uscanner0 to /dev/uscanner15]

or by specifying /dev/ulpt* or /dev/ugen0* or /dev/uscanner*
(examples):

  searching for SCSI scanners:
  checking /dev/ulpt0... open ok
  inquiry for device /dev/ulpt0 failed (Error during device I/O)

  searching for USB scanners:
  ignored /dev/ulpt0 (not a USB device)
  ignoring libusb devices

or, for /dev/ulpt1, and /dev/ugen0* and /dev/uscanner*:

  searching for SCSI scanners:
  ignored /dev/ugen0.00 (not a SCSI device)

  searching for USB scanners:
  checking /dev/ugen0.00... failed to open (Invalid argument)
  ignoring libusb devices

This is even after I removed "uscanner" from my kernel, as
suggested by both
  http://mail-index.netbsd.org/netbsd-users/2008/04/17/msg000624.html
and
  http://wiki.netbsd.se/scanner

Another source suggests "copy libusb20 (installed by default)
over libusb0.1xxx" because "libusb from sourceforge does not
know how to talk with the new UGEN":
  http://archive.netbsd.se/?ml=freebsd-usb&a=2008-12&m=9382607
but I cannot find any such animal as libusb20 on my system.

Meanwhile, www.sane-project.org says that to support PSC 1500,
I need "hpaio", which is included in "hplip".  Our pkgsrc
has neither, but it has "hpijs", which is apparently a
subset of "hplip".  However it is not clear to me whether
any of this is relevant at this point, since I can't even get
"sane-find-scanner" to admit that I have a USB device.  I find
this part of sane-find-scanner's output particularly disturbing:

  ignored /dev/ulpt0 (not a USB device)
  ignoring libusb devices

Why does it think ulpt0 is not a USB device, and why does it
claim it is "ignoring libusb devices"?  My libusb is 0.1.12nb2
from pkgsrc.

Help!

Anne.