A freestyle project triggered remotely via the REST API starts a build even when the project is disabled.
ParameterizedJobMixIn#doBuildWithParameters does not check isBuildable()
What is your version of Jenkins? I cannot reproduce it.
godfath3r Recent Jenkins (any Jenkins 2.x should do), and use the /buildWithParameters endpoint.
Thanks for pointing out Daniel. I've just made a pull request: https://github.com/jenkinsci/jenkins/pull/2431
new pull request available here: https://github.com/jenkinsci/jenkins/pull/2432