Work In Progress
Fixes for a bug report can appear either as patches or a bzr branches. Bzr branches are preferred over patches as it is possible comment on the branch in a merge proposal and diffs can appear in-line in the bug report.
Branches and their status related to a bug report appear beneath the bug's description.
Here we can see that arky's branch, fix-487779, is proposed for merging in to the developement release of the Ubuntu package refpolicy-ubuntu. The reviewer is Ubuntu branches and the review is pending.
Linking to a related branch
It is possible to add a branch to a bug report by clicking on "Link a related branch" in the actions portlet.
The merge proposal is actually performed outside of the bug report - when viewing the branch related to the bug report.
Propose for merging
Click on "Propose for merging".
The target branch should be the bzr branch for the development version of the package - notice the "development focus" text in the screenshot. In the "Extra options" it is possible to specify a reviewer - if it is set to 'ubuntu-branches' you'll want to change it to 'ubuntu-core-dev'.