Incorrect last_updated_by value in Order Headers and Order Lines

I recently joined the community so please advise if I missed to follow any process while posting this item.

We are currently facing an issue in our EBS environment  where we are noticing that occasionally the last_updated_by field  (both in Orders Headers and Order Lines ) is getting stamped with random user id, who swear they never touched the order/line in question, in the latest case it was populated wit a user id who has access to iStore but do not have access to Orders in OM so there is no way the specific user modified the order. Though its not impacting the order progression, its creating confusion in user community and question the system integrity.