autocomplete data-entry on "Additional Namespace Imports" tab using info from the assemblies on the "Additional References" tab.
Typing namespaces is error prone and not validated on the Additional-Namespace-Imports tab. In loading the the "Additional References" assemblies, the namespaces (including spelling and character-casing) could be auto-completed to their correct values. I forgot the case of one character in the namespace, and my only clue was that intellisense wasn't picking up the classes that I expected in the namespace I had mistyped.
This is probably worth doing, although the workaround is simply to enter a type name (without the namespace) into the main code editor. LINQPad will display a smart tag for importing the namespace.