Burndown chart shows incorrect remaining hours

Here below are the steps to replicate the issue that we are having with the Greenhopper v5.2 (JIRA 4.1 Compatible):

1) Created a task(A) (50 hrs) in a version
2) The burndown chart showed 50 hrs remaining
3) The task got broken down into three sub tasks (i.e. A1(20h), A2(20h) & A3(30h)).
4) Removed the estimate (50 hrs) from the main task (A). No task in the version has been started yet. No work has been logged against them.

Now the version burndown chart shows incorrect value of 120 hrs remaining as opposed to what it should (i.e. 70 hrs)

Please advise.

Thanks!