In Mercurial, a new tag means a new commit to the repository.

Mercurial plugin has some code to ignore insignificant changes when polling repository:

if (depchanges.isEmpty()) {

    output.println(Messages.MercurialSCM_non_dependent_changes_detected());

    return Change.INSIGNIFICANT;

}

But this is behavior is not available when using it in multibranch pipelines.

It should be configurable, since many people could be using this behavior to detect new tags and thus triggering deployments.