Misleading SecureStore message with InfoPath Forms Services

In current project we publish an InfoPath 2010 formtemplate to SharePoint 2010 sitecollection. In the formtemplate, multiple controls are populated with data retrieved from a single SharePoint list via application of owssvr.dll and filtering views on that list. The SharePoint WebApplication is set up as Claims-Based. A consequence is that from within InfoPath Forms Services context it is not possible to authenticate via owssvr.dll webservice to the SharePoint list. The proper solution for this is to retrieve the data via Universal Data Connections, and let each UDCX authenticate itself to SharePoint. Either by explicit authentication; that is including the credentials in all UDCX files. But preferably by using the SecureStore; so that the credentials are maintained in a single location and not readable included in the UDCX files.

So far for the theory. In real practice, we encountered a problem with this setup: our formtemplate failed to retrieve the filtered data. In the ULS following message was logged per owssvr.dll/XmlQuery data connection upon opening the formtemplate in browser:

InfoPath Forms Services Maintenance 82lm Information Delegation was attempted for Secure Store application APPL_InfoPathService. (User: 0#.w|domain\useraccount, IP: , Request: http://appl.dev.hosting.corp/Pages/orderform.aspx)

This seems to indicate as if the individual logged-in user has no permission to access/use the SecureStore ApplicationID. Inquiry with Operations refuted that suspicion: the SSS ApplicationID was configured for 'All Authenticated Users'. The actual cause appeared that the service account configured in the SSS ApplicationID no longer had permission/read access to the SharePoint site collection. Instead of above message, I would have preferred a direct 401 or AccessDenied cause-indication in the ULS...