Symptoms

With SharePoint 2010, when I add an item to a SharePoint library using a SmartObject K2 in form creation is sometimes done with the rights of the user, and sometimes with the "System Account" rights!
Can you tell me if this behaviour is related to a setting or an environment variable?
thank you,
 

Diagnoses

This behaviour is linked to the "Authentification Mode" type of the service instance used by the method "Create" or "CreateFolder".
If you choose "Impersonate": the folder or document will be created using the account of the connected user on the form. If the connected user does not have the right, the system will create the object with the System Account.
If you choose "ServiceAccount": the folder or document will be created using the K2 service account.

After check of your smart object "SmoFicheTechnique" we found different Service Instance called by the same SmartObject:
Methods "Create Folder" and "Get Documents" was linked to the Service Instance "Mon Flux ("https...)" was with "Authentification Mode" "Impersonate":
All other methods (including "Create") was linked to the service instance "Mon Flux Porduits Articles" was with "Authentification Mode" "ServiceAccount"

It's why the folders was created with user account and the documents was created with Service Account.

 

Resolution

As you want to have all objects created by the Service account, you just need to:
1) Open The Smart Object Service tester.
2) Expand the node "SharePoint Content"
3) Right click on the service Instance "Mon Flux ("https...)" and choose "Edit Service Instance"
4) Change the first combo box "Authentification Mode" from "Impersonate" to "ServiceAccount"
5) Click on Next Button
6) Click on Update Button.