Why 983-999 status created for Sales order line after Warehouse location confirmation.

I would like to know , why order line status gets cancelled and create new line with location (S..) after Warehouse location confirmation.

And i could see , its not happening every order . example we have two lines with different item in single order and we do warehouse confirmation then only line 2 get spitted and cancelled .

check the below screenshot for your reference.

where after warehouse confirmation , one line was not splitted and cancelled but another item line get cancelled and splitted .

So what is the functionality behind this . And if i want to stop to cancel the line then do we have specific setup