Question about order, order_payment and currencies

[HardKent]

Hi there, 

I am encountering a problem with a third party module called OpenSI  concerning my multi shops and multi currencies Prestashop
When I do an order, these informations (id_currency and conversion rate) are stored in the two tables ps_orders and ps_order_payment 

Actually, with my Prestashop 8.1.7 I'm storing this for exemple

A you can see conversion_rate are different in both tables and that is getting my third party module in trouble cause they expected the same conversion_rate (0.936494)

Is that a normal behaviour from Prestashop to have different values or is that a bug ?
Looking to PaymentModule.php and addOrderPayment method it seems normal  no currency params is passed ....