This commit (https://github.com/jenkinsci/jenkins/commit/7facc7733c7040536d4074a2c5805b75ee1d8f35#core/src/main/java/hudson/model/AbstractProject.java) makes AbstractProject.removeTrigger and AbstractProject.removeTrigger fail because the old Vector is DescribableList now. "removeTrigger" uses remove(int) and I think it shouldn't do it.

java.lang.UnsupportedOperationException
at java.util.AbstractList.remove(AbstractList.java:161)
at hudson.model.AbstractProject.removeFromList(AbstractProject.java:1646)
at hudson.model.AbstractProject.removeTrigger(AbstractProject.java:1622)