Visual Studio shows "the meaning of '<macro name>' does not allow this operation" in unstable manner, but the code compiles OK

[Vasily Kirichenko]

I'm trying to create a macro for generating new classes from string. The simplest thing I started is just generating an empty class with the given name:

macro BuildClassFromString(name)
        Implementation.buildClassFromString(ImplicitCTX(), name)
 
module Implementation
    public buildClassFromString(typer: Typer, typeName: PExpr) : PExpr
        when (typer.IsMainPass)
            match (typeName)
             | <[ $(n: string) ]> =>
                  DefineCTX(typer)
                  def builder = typer.Env.Define (<[ decl:
                      partial public class $(n: usesite) {
                      }
                  ]>)
                  builder.Compile()
             | _ => Message.FatalError ("Type name should be a string literal")
        <[]>

Usage:

BuildClassFromString("My")  
def _y = My()

It compiles OK and VS shows no errors, but if I change the usage code in any way (just add a space anywhere), the following error is shown: 

"Error: AssertionException has occurred when expanding macro 'BuildClassFromString'"

"Error: the meaning of 'BuildClassFromString' does not allow this operation"

If I rebuild the usage project, the errors disappear until the file is changed again. 

So, the question: is it a bug in VS integration or my macro is not perfectly well written (I mean maybe `buildClassFromString` should return `void`)?