HtmlElement.ToString() behavier diff in 32x and 64x

i use very simple code below:

object dom = element.DomElement;  // element is HtmlElement Object
Debug.WriteLine(dom.ToString());

the output in 32x platform target:

"mshtml.HTMLHeaderElementClass" or something other with "mshtml." prefix

the output in 64x:

always is "System.__ComObject".

i confuse about it. how can i get the string value like "mshtml.***" in any platform target?

my environment is:

vs2012, net 4.5 project

thanks