We have an intermittent issue where sometimes the action of linking a third party order to a via a requisition number deletes the requisition number in the original order.
We see the changes in the sales order as 'purchase requisition new = blank' with the culprit transaction ME21N
Our workaround is to cancel the order and PO and start again (which takes minutes so not a massive deal). However, sometimes users don't spot this until last minute at month end, so it turns in to a big deal. The irony is the creation of the PO removes the PR values from the scheduled line, so the SO and PO often sit there for months with 'broken' links and nobody spots it until month end.
There is never anything in the change log, so it must be something that happens as part of the PO creation.
Anyone see this, or behaviour like it? Let me know if you need more info.