I and others had this same question today in the Functional Training class. The trainer indicated that there is no simple "out of the box" way to see who or why when an update happens. But you can install the "Audit Trail" module and then create an audit rule that records a log every time a quantity is updated. It is also said to be an easy and small customization to log the user and a reason for such updates. But customization is out of the scope of the basic training.

This power to create a custom solution is a great thing about OpenERP. But this particular issue seems like an obvious flaw in even the most basic inventory management system. I haven't looked, but I would hope this minor but critical feature is on the project plan somewhere.

1. Install "Audit Trail"
2. Go to "Reporting: Auditing: Audit Rules"
3. Create a new rule with "Change Product Quantity",
4. Check "Log Writes, Log Creates, Log Deletes"
5. Click "Subscribe" (not sure what that does)
6. Save

That's what I remember from the Q&A anyway. It doesn't seem to do anything when I try to replicate for answering you here. But it's probably close enough to figure out the rest.

Ideally the system would automatically tack the user on to any stock move and offer to record a reason with it. It should not be default behavior to move stock without recording who did it.

If I have time to work out the customization to make it work intuitively without the audit trail setup, I'll come back and post here. Until then, lacking a complete solution, I hope these ideas help in some way.

Maybe a more experienced user can describe a solution.