Help with rude 8 year old son | General Dad Chat | Dad Chat Forums

Hi all. I'm a weekend dad, as you may have guessed from my moniker I have my 8 year old son staying for a couple of weeks for the xmas holidays, he lives with his mum when not with me. I usually have him stay 1 weekend a month during school terms and for longer during holidays. He is very well behaved and there are no issues with tantrums, strops etc. There is one problem though, I can't seem to get it into him how important it is to be polite to people. Auntys, Uncles, cousins, friends, my current girlfriend etc. There are no "yes please, no thanks, thank you's" etc. He won't say goodbye to people we've spent the day with and generally seems to wish he was elsewhere on trips out. When questioned about this he says he's happy and enjoying himself. I constantly remind him about saying please / thank you and it sinks in until after a couple of hours. I am always polite to people, strangers, family and friends etc. I make a point of making sure my son hears this when we are out. I have tried speaking to him in a firm voice, calm voice, I ask him questions to ensure he's understood and it all seems ok until he's offered something, then it's just a "yes" or "no" or an answer with no please or thank you. He is not shy, is very outgoing and plays with everyone we are out with. I always correct him straight after an incident and have the talk.
Is this just normal behaviour for an 8 year old boy? and something that just needs persistance & patience? or could it be a sign that there is something wrong?
Thanks