How to freeze the estimate of story?

[Антон Гапеев]

Hello everyone, 

Hope someone faced a similar problem:

1. We are giving an estimate to the user story (let's say 10h),

2. Then we create into this story technical subtask without an estimate.

3. Then when user logging time in a sub-task (let's say 1h) Jira automatically adding this amount of hours (1h) as an estimate of the sub-task, which is affecting an estimate of parent user story. 

As a result estimate of user story increased to 11h compare to original 10h.

How can I skip this way of estimate calculation? 

Regards,

Anton