Symptoms

Workflows originating as K2 service account rather than user who completed form
 

Diagnoses

In looking at the solution, we discovered that the form itself was making a smartobject call to upload an item to the sharepoint list. The workflow was set to trigger off item added in sharepoint, so the user responsible for uploading the document to sharepoint would be shown as the originator of the workflow.
 

Resolution

We changed the service instance to use 'Impersonate', so that it would upload as the user who completed the form. From there, we unchecked the "Enforce Impersonation" box, as that setting requires kerberos. Essentially, if the initial upload fails, it will be retried as the service account, however occurrences of this should be minimal so long as all users accessing the form have rights to the sharepoint list itself.