Bazaar Explorer "Update Working Tree..." on bound branch

[Ewan Milne]

What command does the "Update Working Tree..." option in Bazaar Explorer run?

I have a bound branch, which is not up to date with it's upstream
branch. When I run the above command, I expect the working tree to be
updated to the latest revision in the upstream branch. This is the
behaviour of a command-line "bzr update" on the same branch. But
instead it simply states that the working tree is up to date with the
latest revision in the bound branch, and I need to use "Pull New
Revisions..", which - as expected - pulls the new rvisions from
upstream. But, unless I've misunderstood bound branches, surely update
is the correct action here rather than pull?