fix: don't override reference exchange rate

(cherry picked from commit eaac026)

erpnext/accounts/doctype/payment_entry/payment_entry.py

@@ -335,7 +335,10 @@ def set_missing_values(self):
 		)
 
 	def set_missing_ref_details(
-		self, force: bool = False, update_ref_details_only_for: list | None = None
+		self,
+		force: bool = False,
+		update_ref_details_only_for: list | None = None,
+		ref_exchange_rate: float | None = None,
 	) -> None:
 		for d in self.get("references"):
 			if d.allocated_amount:
@@ -347,6 +350,8 @@ def set_missing_ref_details(
 				ref_details = get_reference_details(
 					d.reference_doctype, d.reference_name, self.party_account_currency
 				)
+				if ref_exchange_rate:
+					ref_details.update({"exchange_rate": ref_exchange_rate})
 
 				for field, value in ref_details.items():
 					if d.exchange_gain_loss:

erpnext/accounts/utils.py

@@ -682,7 +682,7 @@ def update_reference_in_payment_entry(
 	payment_entry.setup_party_account_field()
 	payment_entry.set_missing_values()
 	if not skip_ref_details_update_for_pe:
-		payment_entry.set_missing_ref_details()
+		payment_entry.set_missing_ref_details(ref_exchange_rate=d.exchange_rate or None)
 	payment_entry.set_amounts()
 
 	payment_entry.make_exchange_gain_loss_journal(