If you update your working tree to an earlier revision, then bzr revno reports the latest revision in the repository, not the revision of your working tree. bzr version-info however, reports the revision of your working tree. Why the difference?
> bzr up
M file1.txt
M file2.txt
All changes applied successfully.
Updated to revision 1000 of branch bzr+ssh://bazaar.launchpad.net/~foo/bar/baz
> bzr up -r969
M file2.txt
All changes applied successfully.
Updated to revision 969 of branch bzr+ssh://bazaar.launchpad.net/~foo/bar/baz
> bzr revno
1000
> bzr version-info
revision-id: foo@example.com-20101014072808-xo8f7r0oad9fjelaoi9
date: 2010-10-14 12:58:08 +0530
build-date: 2010-11-05 11:03:20 -0700
revno: 969
branch-nick: baz
Turns out the bzr revno command has two modes: repository and tree. You can execute bzr revno --tree to find the revision of the working tree.