MYSQL/BZR P3: "bzr log -rX" shows more than one mainline revision?

This is a Sun/MySQL - Canonical escalation imported into Launchpad by the Canonical Support Team (internal case 6620).

Original escalation: 2009-11-17 0:04 UTC

We noticed this in May 2009, after upgrading bzr. According to my discussion with Vincent Ladeuil back in May, which I am re-reading now, it *is* a bug and it was introduced in 1.12 or 1.13.
I originally reported this in bug#388794 but it seems this wasn't an appropriate place.
I grab https://code.launchpad.net/~mysql/mysql-server/mysql-6.0-codebase-bugfixing
and I do
bzr --no-plugins --no-aliases log -n0 --show-ids -rrevid:<email address hidden>
When I read the output, I see first, with no indentation, the merge revision tomas.ulin@etc above, ok, then revisions indented (I guess, merged by this merge revision), then, again with no indentation, some other revisions. Like this:
------------------------------------------------------------
revno: 2497.583.12 [merge]
revision-id: <email address hidden>
parent: <email address hidden>
parent: <email address hidden>
committer: Tomas Ulin <email address hidden>
branch nick: mysql-5.1-telco-6.2-merge2
timestamp: Thu 2008-08-07 14:53:02 +0200
message:
  merge
    ------------------------------------------------------------
    revno: 2497.604.48
    revision-id: <email address hidden>
    parent: <email address hidden>
    committer: Tomas Ulin <email address hidden>
    branch nick: cge-6.2
    timestamp: Thu 2008-08-07 13:26:22 +0200
    message:
      remove open optimization in ndb injector thread as it seems to cause problems for concurrent usage of eg reset master
    ------------------------------------------------------------
<cut other revisions all indented>
------------------------------------------------------------
revno: 2617.16.6
revision-id: <email address hidden>
parent: <email address hidden>
committer: <email address hidden>
branch nick: mysql-6.0-ndb
timestamp: Sun 2008-08-10 20:48:50 +0200
message:
  ndb - fix merge error
    in test rpl_slave_allow_batching_basic
------------------------------------------------------------
<cut other revisions not indented>

I don't understand why I see 2617.16.6. Normally, "bzr log -rX" is when you want to see revision X; -n0 is when you also want to see what revisions it merged. Why would it show 2617.16.6?
Another example:
bzr log --show-ids --long -r revid:<email address hidden>
also shows two mainline revisions.