Adding a Timer Intermediate Event to a Task causes "java.lang.IllegalArgumentException: Could not parse knowledge"

Previously raised JBPM-3319 [1] was intended to provide the ability to add a Boundary Event to a Task.
But I'm not 100% if JBPM-3319 is enough to achieve 'able to add a Boundary Event to a Task'. Take an example of the attached process "defaultPackage.newonboarding.bpmn2" where we are expecting to be able to add a Timer Intermediate Event to a Task, but it is not happening as it throws the following ERROR even we try to import the process in JBDS.

~~~
[-1,-1]: Process 'newonboarding' [defaultPackage.newonboarding]: Timer node 'Repeatable Timer' [6] has no incoming connection.
[-1,-1]: Process 'newonboarding' [defaultPackage.newonboarding]: Timer node 'Repeatable Timer' [11] has no incoming connection.
[-1,-1]: Process 'newonboarding' [defaultPackage.newonboarding]: Node 'Repeatable Timer' [11] has no connection to the start node.
[-1,-1]: Process 'newonboarding' [defaultPackage.newonboarding]: Node 'ReminderEmailToAppManager' [5] has no connection to the start node.
[-1,-1]: Process 'newonboarding' [defaultPackage.newonboarding]: Node 'Repeatable Timer' [6] has no connection to the start node.
[-1,-1]: Process 'newonboarding' [defaultPackage.newonboarding]: Node '' [8] has no connection to the start node.
[-1,-1]: Process 'newonboarding' [defaultPackage.newonboarding]: Node 'ReminderEmailToOpsManager' [9] has no connection to the start node.
[-1,-1]: Process 'newonboarding' [defaultPackage.newonboarding]: Node '' [10] has no connection to the start node.
~~~

If we try to execute the process it also throws the following IllegalArgumentException:
~~~
Exception in thread "main" java.lang.IllegalArgumentException: Could not parse knowledge.
at org.drools.builder.impl.KnowledgeBuilderImpl.newKnowledgeBase(KnowledgeBuilderImpl.java:71)
at com.sample.ProcessMain.readKnowledgeBase(ProcessMain.java:26)
at com.sample.ProcessMain.main(ProcessMain.java:17)
~~~

I have tested the attached process with jBPM 5.4.0.Final version and I can confirm that the problem exists in that version too.

[1] https://issues.jboss.org/browse/JBPM-3319