REST API - offset > 500 not working when we include child fields

Hi All,

Using REST API, I am trying to fetch Purchase Orders header and line level fields at once and observed that offset > 500 is not working.

PO Header REST AP: Working as expected

https://XXXX/fscmRestApi/resources/11.13.18.05/purchaseOrders?&offset=501&limit=10&onlyData=true&totalResults=true

PO Line REST AP: Working as expected

https://XXXX/fscmRestApi/resources/11.13.18.05/purchaseOrders/30001134332/child/lines?&fields=LineNumber&onlyData=true&totalResults=true&offset=501&limit=500

But if I combine both header and child data, in below example I have 600 lines for a single PO 'AC001'. offset=0 and limit=500 fetching 500 lines successfully as mentioned below

https://XXXX/fscmRestApi/resources/11.13.18.05/purchaseOrders?q=Status='Open' and ProcurementBU='US Operations BU' and lines.Status ='Open' and OrderNumber ='ABC001'&fields=OrderNumber,;lines:LineNumber,Quantity,Price,;lines.schedules:ScheduleNumber,ShipToLocationCode,;lines.schedules.distributions:DeliverToLocationCode&