[account_invoice_layout] localization missing in invoice items

With the module "account_invoice_layout" I've detected the following behavior :

First I installed both english and french as possible languages.
Then, I defined a partner A with the french language assigned to it.
I also defined a product "prod_en" for which I added the french translation "prod_fr"

The next step is to create a draft customer invoice where I added one item of prod_en.
I leave the invoice in the draft state.

Now under the "Print" icon (GTK client) I select once "Print->Invoices" and once "Print->Invoices with Layout".

What I observe is the following :

For the "Print->Invoices" version all fields are localized in french, which is correct.

For the "Print->Invoices with Layout" version the "Document", "Invoice Date" and "Partner Ref." are not translated while the translation is apparently available.