In the addDynamicUserTask method there is a param with name description, which internally is set as "Comment", which becomes the subject of the task, so it creates task with same 'Description' and 'Subject'. To have unique task description and subject we have to pass it like as:
~~~
data.put("Description", "MyDescription");
caseServicesClient.addDynamicUserTask(containerId, caseId, taskName, subject, actorId, null, data);
~~~