[sane-devel] Epson Perfection1640: Operation not supported

[ael]

I am running Debian testing. I have just discovered that
xsane is now broken after working for 10 years or more on this
Epson Perfection1640.

Xsane fires up as usual, except that there is a new autofocus box
and focus adjustment radio scale. I am pretty certain that this
model has just a binary option for focus:
as on the man page for sane-epson:-
1) Focus  2.5mm above glass, or
2) Focus on glass

I suspect, but so far it only a suspicion, that this is the reason why
when I try to "Acquire a preview", the error message "Operation not
supported."

So has the Epson backend been broken by assumming old models have a
functionalities that don't exist?

But I may be barking up the wrong tree.

Ant suggestions or help? How can I revert to a working version?
Or fix this:-

$ xsane --version
xsane-0.999 (c) 1998-2013 Oliver Rauch
  E-mail: Oliver.Rauch at xsane.org
  package xsane-0.999
  compiled with GTK-2.24.33
  with color management function
  with GIMP support, compiled with GIMP-2.10.24
  XSane output formats: jpeg, pdf(compr.), png, pnm, ps(compr.), tiff, txt

and 
Package: libsane-common
Source: sane-backends
Version: 1.0.32-4

Thanks in advance

ael