S.G.
Leave him be. He has learned a new skill and wants to use it for starters. Second, he knows that when he cries, you come and get him!! So with a new skill he may think that he is missing out on something else where in the house and wants to be part of it. So let him stand up, the thrill will ware off and he'll be easier to take naps again.
Good luck!
S.