Shouldn't Intellisense (autocompletion) be available for members of TypedDataContext such as SubmitChanges?
Currently it does not show up when you start typing it in.
I presume you're using the LINQ-to-SQL driver?
One other thing to keep in mind is that the members won't show if the connection is in the "retrieving schema" state.
I think your second mention must be the issue - perhaps LINQPad should retrieve the schema when a query is created/opened that uses a connection?
Yes, it does automatically retrieve the schema, but there's a delay until the schema arrives.