Sevb32 said:
Exactly! Sometimes the way he holds his head it almost seems as if his expressions change on the mask, even though they don't. Notice how different his helmet looks when he is looking downward like in his opening scene in ANH.

Its funny that! I mean in ESB the helmet-mask is changing all the time because are different helmets. I agree with you that in this particular scene looks pissed off like that the helmet isnt placed correclty from the rush :P

See this: http://thepropden.aokforums.com/esb-and-rotj-vader-helmets-what-do-we-know-vt2464.html

See all pages ang will be amazed how different look the helmet only in ESB. Epesially page 3

-Angel