JIRA doesn't set the estimated time left field to zero when the ticket is closed.

When a ticket is closed, the remaining time on the ticket is not zero-ed out. Lets say that someone opens ticket with an original estimated time as 2 weeks. A week later, this person logs time as 1 week spent. Then next, this person closes the ticket as it was completed earlier than expected. However, if this person forgets to set the time remaining to zero, JIRA lets the remaining time estimate stay at where it was (1 week). Once the ticket is closed it can't be updated unless it is re-opened. Now this shows up in the time tracking report as time remaining on the project task, which is not accurate. At the same time closed tickets can't be edited, so its a problem.