The calendar plugin currently depends on version 1.4. Given the way that classes in Confluence dependencies are given precedence over jars bundled in plugins, this is causing the Calendar plugin to fail (as it is loading a version 0.98 class).

We only have two usages of joda time. We construct a DateMidnight object in ContentEntityObjectHiberndateDao and AbstractHibernateAttachmentDao. The constructor that takes in a long parameter is still present in 1.4, so this is a safe upgrade.