Collaboration/Child task business data issue

Can parent and child task have different business data.?

I have a use case where the parent task has Document A as business data while child task has Document B as business data.
And I’m using the out of box API to queue a child task by transforming Document A to Document B, and queue the child task with Document B as TaskData and parentTaskId as TaskID of the parent task.
The queueTask service is successful and I see a new taskID also generated.
Unfortunately, when I getTask with the taskID of child, I get TaskInfo of the child but TaskData of the parent.
Any idea what is going wrong? Am I missing something.?

P.S: wM version 9.12