scanadf with Brother ADS-2800W scanner ("brother4" driver) feeds one more page than requested through scanner

[Jonathan Kamens]

I am using a Brother ADS-2800W scanner with the "brother4" SANE driver (which I believe is provided by Brother). I want to put a stack of documents into the scanner and scan them in separate scanadf jobs. When I specify "-s 1 -e 1" as arguments to scanadf, scanadf only produces one output image, BUT it feeds two pages through the scanner, i.e., it's feeding through a second page for which an image is never produced.

I don't know if this is a SANE bug, a bug in the brother4 driver, or a problem with the abilities of the scanner itself, but I thought I should start by filing this bug and then perhaps y'all can guide me through next steps to help isolate the root cause of the issue.

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: sane 1.0.14-12build1
ProcVersionSignature: Ubuntu 4.15.0-33.36-generic 4.15.18
Uname: Linux 4.15.0-33-generic x86_64
NonfreeKernelModules: nvidia_modeset nvidia
ApportVersion: 2.20.9-0ubuntu7.2
Architecture: amd64
CurrentDesktop: ubuntu:GNOME
Date: Sun Aug 26 15:50:35 2018
InstallationDate: Installed on 2016-01-16 (953 days ago)
InstallationMedia: Ubuntu 15.10 "Wily Werewolf" - Release amd64 (20151021)
SourcePackage: sane-frontends
UpgradeStatus: Upgraded to bionic on 2018-04-19 (129 days ago)