Question on notification :Acknowledgment response from supplier says it is auto-approved

We are in 12.1.3, using i supplier , our buyers are getting notifications saying "Acknowledgment response from suplier_name ,Incorporated for Standard Purchase Order 73611 ..have been auto-approved"

We are not setup to auto approve or auto accept  changes done by suppliers and the notification says "Acknowledgment... and not Change so when do you get these type of notifications?

Thanks

Rahul