There was a similar problem with the git plugin. It was fixed so that the variable (Choice Parameter in my case) is resolved as the default value, when polling.
Now I need to have a separate Polling Job that triggers my main job, which seems a bit stupid. I only want to build automatically if there is a push in the default branch,
and also be able to build manually the other branches.
I have global jenkins variable. I use it to set mercurial branch to poll scm changes. Job start if there is push in repository.
But if I see polling log it show variable name instead of its value:
Started on Jun 21, 2013 11:25:49 AM
[myjob] $ hg pull --rev ${branch_to_update_default}
pulling from https://myrepo
no changes found