Why does Scrumwise add an extra task sometimes?
This happens if you add a task to a backlog item that has already been estimated and doesn't yet have any tasks. In this case, Scrumwise assumes that the task you are adding represents more work, in addition to what you have already estimated in the backlog item. Therefore, Scrumwise adds an extra task to represent the already estimated work, in addition to the new task that you are adding. The extra task will have the same name and estimate as the backlog item itself.
If you prefer not to have an extra task added like this, go to your personal account page in the settings in Scrumwise, and uncheck the setting "Add additional task in backlog items in some cases" in the "Other settings" section. Alternatively, just delete the extra task if you don't need it.