title: Accessing a member on Form may cause a runtime exception because it is a field of a marshal-by-reference class
body: <blockquote>
    <p>Accessing a member on Form may cause a runtime exception because it
    is a field of a marshal-by-reference class</p>
  </blockquote>
  
  <p>I know what this warning is and know how to solve it.</p>
  
  <p>My question is why could this cause a runtime error?</p>