The actual cause of the NumberFormatException is https://jira.jboss.org/jira/browse/JBPM-2478. When configured with Spring, jBPM looks in the Spring context for autowiring candidates based on class type when instantiating the RepositoryCache, in this case a Map. The first Map it finds is the Spring systemProperties bean and injects this, when it really should just leave the deployment and deploymentClassLoaders as empty Maps.
Is there a way to turn jBPM autowiring off, at least for specific classes?