User field of completed requests lost from long running query that timed out

Loaded up a dataset of ~200M items and created a primary index on it via the query workbench.  The query timed out after 10m as per the workbench settings but the completed_requests doesn't show the user (see screenshot).

This should be reproducible with any query that runs for a long time and then times out in the workbench, the primary index creation was just an easy way of achieving that.

I have also tested shorter running queries with a much lower timeout and the user is displayed properly so there is something specific to long-running timed out queries.  

One thought from Marco Greco was that the user field may be getting "recycled" before the query times out and therefore not available when the timeout happens.

This could be seen as both a security risk as well as an operational challenge if an administrator is not able to see which user executed a very long-running query.