I have a strange and, it appears UNIQUE situation. My boy is almost 3 years old and he's done VERY WELL in PP training but he acts VERY strangely towards my 24 year old son. My son has obviously been around my dog but only when he came home from college, but he's been here since May of 2012 so he's been around more than ever.  When my son WOULD come around he didn't really have anything to do with my dog but he was never mean towards him, he'd half pet him a little bit but very briefly. Now, here's the situation, my son comes over on the weekends now and when he does my dog almost DETECTS him pulling up because he IMMEDIATELY gets up and starts barking almost viciously and when my son comes in he barks even more in his deep boy bark but when my son approaches he backs away at times with his tail between his legs, he used to play bow but NOW it's almost in fear. Every so often Butch will get up and go to my son's open door and start barking at him and TODAY I was sitting in my son's room and I called Butch in and he was fearful of coming in and I had to get up and meet him and get him to come on. Later this evening Butch did his same loud barking when he heard my son pull up and come in, now; every now and then my son will play with Butch by play bowing and chasing him around but when he did it today Butch backed away, then bowed, put his tail between his legs and ran away. Butch then came back and when my son tried playing with him by bowing Butch ran away AGAIN and when my son squatted and went towards him, Butch dropped all the way down in fear/submission but he did NOT show his belly, I've NEVER seen him do THAT. I know this is a LOT of reading but HELP can someone, ANYONE give me some help/ADVICE? THANKS IN ADVANCE.