Extremely funny behavior .. could be a bug?

[seany via Digitalmars-d-learn]

consider the following :

in file a.d

module a;

class class_a
{

    struct RESULT{
    string[] raw;
    void* res;
   }


RESULT r;

void dothing()
{
    r = new RESULT;

    string aa = "string";

    r.raw ~= aa;
    r.res = cast(void*) aa;
}

}


in file b.d

import a;    // import path is okey

class class_b;
{

    void doThings(class_a * ptr_a)
   {
      class_a A = &ptr_a;
      writeln(A.r.raw[0]); // prints aa;
      writeln(A.r.res);    // fails : 
core.exception.OutOfMemoryError@(0)
                               // but if i do comment the line :
                               // writeln(A.r.raw[0]); out, then 
works
   }
}


in file c.d

import a;
import b;

void main() {

clsa = new class_a;
clsb = new class_b;

clsa.dothing();
clsa.doThings( & clsa);


}


I can not find a reason why accessing A.r.raw will erase (invoke 
the garbage collector) to remove A.r.res. Please help.