NCrunch works fairly low-level in its collection of code coverage information, which can sometimes create ambiguity around LINQ statements - there's some more information about the difference between physical and logical test coverage here.

My first thought in this case is that the black dot represents code the compiler has generated for the LINQ Select statement, in which case the code wouldn't be executed if the enumerable had no data behind it. Is there any data stored in this enumerable? If not, does adding some data make any difference in the code coverage?