I've been confused about the way that branches are treated when they are merged back into the branch that Bitbucket denotes the "Main branch" (master by default). In particular, the Commits visualization (https://bitbucket.org/<user>/<repo>/changesets does not show the "lozenge" for commits on such branches, and the individual-commit view (https://bitbucket.org/<user>/<repo>/changeset/<commit>) does not list the branch under the "Branches" list. I would strongly prefer to see the "raw" git repo, e.g. as would be shown by gitk --all.
For a (contrived, and slightly messy) example, see https://bitbucket.org/mbc/test2/changesets. Branch b is not indicated at all, even though it exists in the repo, only because it is merged back into the "Main branch" (master). Similarly, commits of branch d before its merge into master are not indicated, but commits after the merge are. Branch f -- after master -- is indicated as I would expect.
In the above example, note especially the orphaned DAG consisting of c and e: these are visualized exactly how I would expect, and I would like the option to have master and branches touching it to be visualized in the same way.
Personally, I find the concept of a "Main branch" to be an unnecessary limitation, but I would be happy enough to have the option of just turning it off.