The mercurial plugin provides a branch field. I would expect that if this is
used, the slave's copy of the repository would be updated to the specified
branch. It is not, instead it is left at the default branch.

I created a simple repository with a named branch. The console output is
Started by user anonymous
[workspace] $ hg update -C .
0 files updated, 0 files merged, 0 files removed, 0 files unresolved
[workspace] $ hg --config extensions.purge= clean --all
[workspace] $ hg incoming --quiet --bundle hg.bundle --template "<changeset
node='

{node}

' author='

{author|xmlescape}

' rev='

{rev}

'
date='

{date}

'><msg>

{desc|xmlescape}

</msg><added>

{file_adds|stringify|xmlescape}

</added><deleted>

{file_dels|stringify|xmlescape}

</deleted><files>

{files|stringify|xmlescape}

</files><parents>

{parents}

</parents></changeset>\n"
-r branch1
[workspace] $ hg pull -u hg.bundle
pulling from hg.bundle
searching for changes
adding changesets
adding manifests
adding file changes
added 1 changesets with 1 changes to 1 files
0 files updated, 0 files merged, 0 files removed, 0 files unresolved
Finished: SUCCESS

The workspace repository isn't updated to the requested branch
C:\Users\ben\.hudson\jobs\HudsonMercurialTest\workspace>hg branch
default

C:\Users\ben\.hudson\jobs\HudsonMercurialTest\workspace>hg identify
1333768e2c9e

C:\Users\ben\.hudson\jobs\HudsonMercurialTest\workspace>hg log
changeset: 2:a723eea10923
branch: branch1
tag: tip
user: Ben Mathews <Ben.Mathews@HexagonMetrology.com>
date: Tue Jun 16 10:34:57 2009 -0600
summary: branch 1 commit

changeset: 1:1333768e2c9e
user: Ben Mathews <Ben.Mathews@HexagonMetrology.com>
date: Tue Jun 16 10:32:51 2009 -0600
summary: 'test'

changeset: 0:c9ec671340fe
user: Ben Mathews <Ben.Mathews@HexagonMetrology.com>
date: Tue Jun 16 10:31:53 2009 -0600
summary: 'test'

Either as part of the hg pull command or as a seperate command, the repository
needs to be updated to branch1.

Thanks