What Block Isn't Covered?

Visual Studio 2013 is showing my code coverage for this (simplified for this example) object as missing a block:

As far as I know, that if should have exactly two states. Pass and fail. And debugging my tests shows that each of those conditions is executed once. Specifically with these two tests:

[TestMethod]
public void CanNotHaveNegativeServiceWindow()
{
    // arrange
    var request = new CreateCaseRequest
    {
        ServiceWindowStart = new DateTime(2014, 12, 31, 12, 00, 00),
        ServiceWindowEnd = new DateTime(2014, 12, 31, 11, 00, 00)
    };

    // act
    var result = request.GetValidationErrors();

    // assert
    Assert.AreEqual(1, result.Count());
}

[TestMethod]
public void CanHaveServiceWindow()
{
    // arrange
    var request = new CreateCaseRequest
    {
        ServiceWindowStart = new DateTime(2014, 12, 31, 11, 00, 00),
        ServiceWindowEnd = new DateTime(2014, 12, 31, 12, 00, 00)
    };

    // act
    var result = request.GetValidationErrors();

    // assert
    Assert.AreEqual(0, result.Count());
}

One test validates the positive result of that specific if condition, the other validates the negative result. What block isn't covered? What logical condition exists that I'm missing?