Sale order line containing service duplicated on invoice

Create a sale order with 2 lines:

- 1 product type stockable product (like PC1) with qty 2
- 1 service (like EMPL) with qty 3

Picking Policy : Partial Delivery
Shipping Policy : Invoice From The Picking
Invoice on : Shipped Quantities

On the delivery order, process one element of PC1. It will create a new delivery order in state done.
Process the last element of PC1 in the first delivery order. You have a second delivery order in state done

Select both delivery orders in view list and click create invoice in actions. Group the invoices (well, even if you don't, the problem will persists) and check the invoice:

You have 4 lines :
2 x 1 line with your stockable product with the right qty : 1
2 x 1 line with your service but both have a qty of 3

You pay your service twice.

This bug is also present in v6.1