Launchpad is used for tracking bugs, improvements and new features. See https://bugs.launchpad.net/bzr-explorer.
After raising a bug, a developer will triage it to give it a priority. They may also change the project the bug is related to if the bug is caused by a lower level product, e.g. QBzr or bzr itself.
When a fix for a bug is available in a branch, it will be marked as “Fix Committed”. When a fix is landed into the trunk, it will be marked as “Fix Committed.”