i agree that it's normal. i put it in the category of asserting independence (well, that's how it seemed here!)...it's no fun having your nappy changed when you were in the middle of a game/playing etc. and it's just another thing that someone else decides the timing of (itms?). i agree with distraction techniques. do you think he'd understand if you explained that he could do something/return to his game after it was done? i often let DS get his nappy, open/close the wipes container etc so he was part of the whole process.

but in the end, i found around 18 months a challenging time for behaviour in general because DS' language wasn't great yet so he was (i guess) frustrated that he couldn't communicate in words. now, a year on, he'll tell me he doesn't need a clean nappy but we can talk about it more & i can offer two places (for eg) that he can be changed & he gets to choose.

i had a friend who changed to pull ups around that time because her DD would refuse to lie down for nappy changes. that seemed to solve their issues (although when I babysat, she would lie down for me - cheeky monkey!)

good luck - i hope this stage passes quickly!