codetree does not update the branch tree revno on existing branches that do not specify a revno

If no revno is specified when an existing branch is "updated" bzr pull happens but bzr update does not leaving the branch tree version at which ever revision was orginally checked out. This is not intuitive.

Example:

# Revno specified no existing branches
~/tmp/test⟫ cat collect
interface-mangler lp:~canonical-sysadmins/canonical-is-charms/interface-mangler;revno=4,overwrite=True

~/tmp/test⟫ codetree collect
Branching lp:~canonical-sysadmins/canonical-is-charms/interface-mangler to interface-mangler
Checking out revision 4 of lp:~canonical-sysadmins/canonical-is-charms/interface-mangler

~/tmp/test/interface-mangler⟫ bzr st
working tree is out of date, run 'bzr update'
~/tmp/test/interface-mangler⟫ bzr revno
6
~/tmp/test/interface-mangler⟫ bzr version-info
revision-id: <email address hidden>
date: 2014-08-04 23:49:27 +0000
build-date: 2015-03-26 14:17:30 -0700
revno: 4
branch-nick: interface-mangler
# This is expected behavior

# No revno specified with existing branches
~/tmp/test⟫ cat collect-upgrade
interface-mangler lp:~canonical-sysadmins/canonical-is-charms/interface-mangler;overwrite=True

~/tmp/test⟫ codetree collect-upgrade
Updating interface-mangler from parent (bzr+ssh://bazaar.launchpad.net/~canonical-sysadmins/canonical-is-charms/interface-mangler)

~/tmp/test/interface-mangler⟫ bzr st
working tree is out of date, run 'bzr update'
~/tmp/test/interface-mangler⟫ bzr revno
6
~/tmp/test/interface-mangler⟫ bzr version-info
revision-id: <email address hidden>
date: 2014-08-04 23:49:27 +0000
build-date: 2015-03-26 14:18:31 -0700
revno: 4
branch-nick: interface-mangler
# Here we would expect version-info to show us revision 6 as the branch was "updated" but we get 4 from the original checkout.

# Revno specfied with existing branches
~/tmp/test⟫ cat collect-upgrade-specific
interface-mangler lp:~canonical-sysadmins/canonical-is-charms/interface-mangler;revno=6,overwrite=True

~/tmp/test⟫ codetree collect-upgrade-specific
Updating interface-mangler from parent (bzr+ssh://bazaar.launchpad.net/~canonical-sysadmins/canonical-is-charms/interface-mangler)
Checking out revision 6 of bzr+ssh://bazaar.launchpad.net/~canonical-sysadmins/canonical-is-charms/interface-mangler

~/tmp/test/interface-mangler⟫ bzr st
~/tmp/test/interface-mangler⟫ bzr revno
6
~/tmp/test/interface-mangler⟫ bzr version-info
revision-id: <email address hidden>
date: 2015-03-20 15:18:57 -0700
build-date: 2015-03-26 14:21:52 -0700
revno: 6
branch-nick: interface-mangler
# This is expected behavior