fix: Exchange rate on MR to PO creation for muticurrency POs (#39646)

diff --git a/erpnext/stock/doctype/material_request/material_request.py b/erpnext/stock/doctype/material_request/material_request.py
index e784b70..02fbd3d 100644
--- a/erpnext/stock/doctype/material_request/material_request.py
+++ b/erpnext/stock/doctype/material_request/material_request.py
@@ -462,6 +462,7 @@
 		postprocess,
 	)
 
+	doclist.set_onload("load_after_mapping", False)
 	return doclist