Symptoms

Modified by for the list item is not the user that created it although no one else has modified it.
 

Diagnoses

IF there are any changes made to the list data, ie update column or anything from within a K2 workflow, this will have to happen under the context of the “K2 Account”. K2 Account is the account used to provision K2, ie the global admin account and the account used to Register the K2 App. This account owns the Oauth token for K2 to have consent to make changes in SharePoint.

So any changes made to a list using K2 workflow will use his account as the modified / created etc.
 

Resolution

This is by design at the moment.

logged as a feature though – the feature is to see if we can rather use the users account that initiated the K2 workflow rather than the actual executing account which must be the Oauth token owner to have access to SharePoint.