V13/V14: Create an SO followed by SI and DN

Hi all,
On V14 i have created an SO and created after the DN for the same. Created the SI and after that the Customer decided no longer to keep the Item…

So i created a RETURN for the SI and created a RETURN for DN.
Now my point is why when i return to the Sales Order i can create a new DN but i cannot create another SI!

As you can see i have one INVOICE (actually is the RETURN) and i have 2 DELIVERIES (DN and RETUN DN). On the DN i can create but on the INVOICE i cannot (no PLUS button).

If we do the same process on Purchase ORDER it will allow me to create a Purchase Invoice and a RETURN of the PI and also allow me to create another Purchase Invoice