Not necessarily true, pain can come out in a number of ways. Drastic change in personality is one of them. I wouldn't totally cross of pain if he is already sensitive. I personally would rather rule out pain first with my vet, then start really getting on his case if he is in fact just not listening.
Thanks for the suggestion, but I know he's not in pain. He's showing no signs of it at all and his personality hasn't changed one bit. Walking forward was an issue we had to work through when I first got him and now the only time he does this is when we're in the jump field, which is where we've done most of our riding lately. Out on the trails and around the barn, he has no issues whatsoever (other than getting excited and spooking occasionally).