Visual Studio marks code just after "case variable:" unreachable

Question

I have a switch statement with multiple cases:

ConversionState state = ConversionState.Start; // enum
for(int i = 0; i < source.Length; i ++)
{
    switch(state)
    {
        case ConversionState.Start:
            state = ConversionState.Name; // <-- warning here
            name += source[i]; // source is a string
            break;
        case ConversionState.Name:
            if(source[i] == ' ') // <-- warning here
            {
                name = name.ToLower();
                if(name[0] == '/')
                    name = name.SubString(1);
                state = ConversionState.Between;
            }
            else
                name += source[i];
            break;
        case ConversionState.Between: // no code in this case statement, yet to be implemented
            break; // <-- warning here
    }
}

I get a warning on the three marked lines: "unreachable code detected". The very first statement after a case can't be unreachable, can it? My questions are:

1. Is something wrong with my code, or is the warning wrong?

2. If VS2015 thinks a code snippet is unreachable, does it get removed when I compile with optimizations on? If not, should I just ignore this warning?

3. Does this warning mean that the marked line is unreachable, or that the whole case is unreachable?

PS: I know that the current code can be rewritten without switch, and that would solve the problem, but the future code that will be added will make it - MUCH - easier to maintain using a switch.

Edit (requested by amit dayama):

private enum ConversionState
{
  Start, Between, Name, Argument, Switch
}

The enum is inside the class that has the method that contains the originally posted code.

Edit 2: The very first line of the method this code is in was throw new NotImplementedException();. Apparently, this makes Visual Studio mark the first line of every case in every switch in the method unreachable, but nothing else, and, interestingly, not the entire code following the exception.

Answer 1

I have checked your code and everything compiles and builds on my side, using VS2012. I now there are a few problems with VS2015, with a lot of false positives in Error List Window.

So question 1: from my side, your code is correct.

Question 2: Not entirely sure, but believe that id does not remove it for optimization. I can be wrong, but the reason for the warning is that you address it and not the compiler. I will add comment when I found the correct answer for you.

Question 3: the line not the entire case.

PS: maybe you can try and add the curly braces into some of your if and else statements. I know they are not required for one liners, but they might be causing the specific behavior in VS2015