Workflow 2010: Output variable data is empty from "Get data from user" task in Workflow Designer 2010

Question

I am designing a workflow to collect data from different users. The workflow is as follows:

1. Item added to the list.
2. "Collect data from User" task assigned to user 'A'. User A fill the form and select the user (say User 'B') for further information and then submit it.
3. Get the data from User 'A' task form output variable and save it into a list.
4. "Collect data from User" task assigned to user 'B'. User 'B' fill the form and submit it.
5. Get the data from User 'B' task form output variable and save it into the list (same list used for User 'A' output data).

Problem: In step 5, the variables are empty.

Analysis: I used "Start Approval Process" task in step 4 and found that the even if I approve or reject the task, the outcome is Completed which is used for "Collect data from User" in step 2.

I think that the variables still have the data from step 2 and they are not updating in step 4 that's why the variable is empty.