Finally, I found the root-cause of this issue. It is a complete bug of Oracle related to view "por_lines_v".
Oracle view has a connection to oe_order_headers ooh where prh.segment1 = ooh.orig_sys_document_ref(+).
It means that number of rows are populated to I-Procurement page is related to number of orders which has the same value for order reference for sales orders.
Currently requsition numbers are around 25000. But there are some orders (Internal orders, so reference numbers were populated by Oracle, not from customer) has the same numbers.