requesting diff of one file gives output of all changes

Binary package hint: bzr

The current lp:ubuntu/python-boto branch is a bit screwed up (to be fixed in bug 788736), but it illustrates a bug in bzr.

$ bzr diff -r tag:1.9b-1..tag:1.9b-1ubuntu1 debian/rules | diffstat -p1
 NEWS | 19 ----------
 changelog | 81 ------------------------------------------
 compat | 1
 control | 26 -------------
 copyright | 37 -------------------
 pyversions | 1
 rules | 115 ++++++++++++++++++++++++++++++++-----------------------------
 watch | 3 -
 8 files changed, 61 insertions(+), 222 deletions(-)

Above I requested a diff of a single file (debian/rules) but the entire diff from the two revisions was given.

I've attached the .bzr directory of lp:ubuntu/python-boto for reproducibility. Grab the attachment, then:
tar -xvzf python-boto.tar.gz
cd python-boto
bzr revert # to restore the files I deleted to save space
bzr diff -r tag:1.9b-1..tag:1.9b-1ubuntu1 debian/rules | diffstat -p1

ProblemType: Bug
DistroRelease: Ubuntu 11.10
Package: bzr 2.4.0~beta2-2ubuntu1
ProcVersionSignature: Ubuntu 2.6.39-3.9-generic 2.6.39
Uname: Linux 2.6.39-3-generic x86_64
Architecture: amd64
Date: Thu May 26 13:18:55 2011
EcryptfsInUse: Yes
InstallationMedia: Ubuntu 10.04 "Lucid Lynx" - Beta amd64 (20100318)
PackageArchitecture: all
ProcEnviron:
 PATH=(custom, user)
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: bzr
UpgradeStatus: Upgraded to oneiric on 2010-11-15 (191 days ago)