Obsoleted commits show "default" as own named branch, regardless of actual one (BBCC-502)

In the commit view page of Mercurial repositories, obsoleted commits always show "default" as own named branch, regardless of actual one.
This can be reproduced by steps below with enabling changeset evolution.

1. make a commit on a named branch "FOO"
2. push the new commit to the repository on Bitbucket cloud
3. rebase this commit to another named branch "BAR"
4. push the rebased commit to the repository on Bitbucket cloud
5. visit "commits" page of the commit made at (1), which is already obsoleted at (3)

Obsoleted commits are never be pull-ed any more, and never appear in main history pages. Therefore, this is minor (or trivial ?) bug, but might confuse users.