Changes to Currency Exchange Rate affects Price Rate in Sales Invoice

Hi, my company currency is USD. I face a problem when generating a Sales Order to Sales Invoice in non-company currency.

When I create a Sales Order in say April, the currency exchange rate for that month would be used for that SO.

When I create a Sales Invoice from that SO in say July, I want to use the currency exchange rate for that month for tax purposes. However, when I change the currency exchange rate, somehow the price rate for the items also changed. This is rather surprising for me as I want the price rate to remain the same but just need to change the currency exchange rate.

I tried to disable options like price rules, take out tax templates, etc, but to no avail.

Just wondering if I am doing something wrong or have understood the currency exchange rate and price rate relationship wrong?

Appreciate any help on this matter!

PS: Have searched through the forum but not seen anyone having this problem/concern. I am on ERPNext: v13.35.2 (version-13) / Frappe Framework: v13.35.2 (version-13)

Managed to solve this problem by selecting a “Price List” that is based on company currency (eg. Standard Selling).

This is not a very neat solution as it confuses the user since he/she needs to choose a price list that is not based on customer currency. But it works for me for now.

Wonder if anyone came across this issue?