Currency Rates being changed automatically

We are using multi-currency with Live exchange rates switched off.   We manually add the exchange rate to our overseas purchases when we set up the purchase order.

When billing, the exchange rate used to reset to zero and we manually updated it to the current rate which we get from our bank.

Since updating to AR 2022.7, the rate no longer starts at zero when creating the PO, or resets to zero upon invoicing the PO (but also changes from what it was originally set to).  It is being adjusted automatically to an unknown rate, without any manual input AND with 'live exchange rates' switched off.

Can someone identify what/why this is happening, and where the rate MYOB assigns is being pulled from, considering that live rates is switched off?

Thanks.