Manually filling existing contactaccount fields on a Lead form automatically populates emailphonecompany name fields

Hi,

Facing an issue with a Lead form in a latest Dynamics 365 on-line environment.

When I fill existing contact (parentcontactid) or existing account (parentaccountid) fields manually it automatically triggers internal OOB JS that retrieves those records and populates various information fields on a form. 

And this is an unwanted behavior since emptying those fields doesn’t trigger the automatically populated fields to empty themselves as well.

Can I somehow just turn off this behavior?