The TaskInstance gets its description from the Task object. You can set the Task description using the attribute 'description' in the 'task' element:
<task name="theName" description="theDescription" swimlane="theSwimlane" />
I have created the issue:
Yes, I know that you can set the description through the task element, but then the description of every TaskInstance originating from the same Task has the same description. Imagine having 20 task instances in the task list, all originating from the same task (not at all uncommon), and they all look exactly the same... There HAS to be a way to provide the description for each task instance.
Besides, why have a property that you can neither get nor set? This is clearly a bug.
If you want the description of the originating Task, you can always get it right there - from the Task.
Is it possible to change the jpdl in a future version so that the description can be set as a tag in case it has complex CDATA? THis isn't killing me now, but I was wondering about it as I have been playing a bit in the sandbox.