Issues with changing the date of a cloned task

[GB]

To save time, we have cloned some similar tasks. 

Now the start and end dates of the clones must be changed as we have some changes inside our project. Unfortunately the start and end dates cannot be changed, as Jira always jumps back to the dates of the initial task. 

I would like to be able to set the start and end date of the clone seperately. Is that possible?