account_invoice_change_currency conversion doesn't calculate value with the manual rate

[tv-openbig]

account_invoice_change_currency onversion doesn't calculate anything

Module
account_invoice_change_currency

Describe the bug
There is no currency conversion in the invoice, after changing to a foreign currency
and applying a individual currency rate which is different from the current
Odoo standard currency rate.

To Reproduce
Affected versions: at least 14.0

I switch to a german company.
Main currency is EUR.
Current Currency rate is 0.90000 in Accounting / Settings / Currency
I have a product with a purchase price of 100,00 €
I want to create a invoice in USD.
If i switch in customer invoice to USD and apply the manual rate 1.50000 i
would expect that Odoo would re-calculate my invoice line from 100,00
€ to 150,00 USD.

For sure i also tried to save the new individual currency rate before adding a new Po line.

Expected behavior
If i switch in my invoice to USD and apply the manual rate 1.50000 i
would expect that Odoo would re-calculate the invoice line from 100,00
€ to 150,00 USD.

Furthermore the account move should have 100 € in main currency and 150 USD in foreign currency.

Additional context

I have recorded a video:
https://drive.google.com/file/d/15cEIEgm0SHZwmpwC6m-rcrWO1gkjO-UE/view