Workflow bacground process and autoinvoice running at same time

Hi,

We have seen some cases where multiple invoices got created for same order although as per grouping rule it should have been just a single invoice. Grouping rule is based on order_number and delivery_id and for that order there is a single delivery_id. The only anamoly we could see is that autoinvoice(or wrapper around autoinvoice) was scheduled to run at same time as workflow background process. Is there a chance that this could have created the issue. We are not able to duplicate this in a controlled way