Using the latest JIRA plugin (1.29) doesn't work in the latest version of Hudson (2.1.2). With "Update relevant JIRA issues" checked in a job's config, if a commit occurs with a valid JIRA number, the build fails with this:

Updating ECOM-8428
FATAL: hudson.scm.ChangeLogSet$Entry.getCommitId()Ljava/lang/String;
java.lang.NoSuchMethodError: hudson.scm.ChangeLogSet$Entry.getCommitId()Ljava/lang/String;
at hudson.plugins.jira.Updater.getRevision(Updater.java:263)
at hudson.plugins.jira.Updater.submitComments(Updater.java:136)
at hudson.plugins.jira.Updater.perform(Updater.java:91)
at hudson.plugins.jira.JiraIssueUpdater.perform(JiraIssueUpdater.java:29)
at hudson.tasks.BuildStepMonitor$3.perform(BuildStepMonitor.java:36)
at hudson.model.AbstractBuild$AbstractRunner.perform(AbstractBuild.java:630)
at hudson.model.AbstractBuild$AbstractRunner.performAllBuildSteps(AbstractBuild.java:608)
at hudson.model.AbstractBuild$AbstractRunner.performAllBuildSteps(AbstractBuild.java:584)
at hudson.model.Build$RunnerImpl.post2(Build.java:159)
at hudson.model.AbstractBuild$AbstractRunner.post(AbstractBuild.java:553)
at hudson.model.Run.run(Run.java:1391)
at hudson.model.FreeStyleBuild.run(FreeStyleBuild.java:46)
at hudson.model.ResourceController.execute(ResourceController.java:88)
at hudson.model.Executor.run(Executor.java:145)