We had a situation yesterday where two engineers picked up the same ticket within a minute of each other and assigned it to themselves. The second users changes clobbered the first without any type of warning, so they both worked on the ticket for the whole day, and as a result we had a full days loss of engineer productivity. Jira should either disallow stale updates (i.e. if the ticket state has changed since the user started editing it, do not accept the update), or provide some way for the user to manually merge the changes.