Normally when creating/deleting a worklog we don’t ask user about how to handle remaining estimate. But when moving worklogs from one issue to another using "bulk update" feature, we don't update remaining estimate of original issue and new issue.
User should be given about how he/she wants to handle remaining estimate when using moving worklogs but this is more difficult to implement than it seems. As a simple case, we can use "Auto" feature, which increases/decreases according to 'Time Spent'. Updating issue may be a problem though.