I found out a behaviour on statement which is not consistent:
On simple case with company with same currency as their bank:
When you have a origin statement line of +100€ and you create a line and select your invoice of +50€, the amount updates to 50€.
Since here, all ok, let’s jump to a bit more complex example:
Company with currency on euro.
Bank in dolars and the journal defined on dolars. Also currency rates are activated.
On a statement with orgin line on date 14/12 (1€=1.1309$) with amount +140$ and you select your invoice of 50€ the amount on the line remains the same (+140$).
The ideal should be to update the amount once the invoice selected to 56.56$.