Yep. Producer and Holm-made are right on. Folks tend to overdraw when they're checking their draw length with a clothes pin or marked arrow. When they're not thinking about it and just shooting, the draw often shortens perceptibly.
Jim: As Pdk notes, if you shoot with a high wrist regardless of the grip style, your draw length won't vary, at least not very much. But, if you shoot a recurve high or medium wrist and try a straight grip longbow and shoot it low wrist, your draw will shorten considerably.