Copy from the first row is not working in case of "rate" field in child table of delivery note

I am coping the data of first row on add new row button click of child table of delivery note. All the fields are getting the values exactly as the first row. but I can’t copy the ‘rate’ field. I think it’s being overwritten by the erpnext default function and again set to standard selling rate.

I would like to copy the rate field from the first row on add new row button. What can i do for that ?

i would like to know too, any idea?