Unfortunately, this looks like a bug. Even more unfortunately, there seems to be no workaround. The issue only exists when using SelectMany(); maybe you can reformulate this query to use Join()?
We will provide a fix for this issue in one of our next versions, but I cannot give you a concrete date yet.
Thanks for reporting this issue with us; I've updated your Telerik points.
OpenAccess ORM is now Telerik Data Access
. For more information on the new names, please, check out the Telerik Product Map