It might not be required in the AIP but if he has given you a clearance then asked you to report leaving a level for further clearance there could be a particular reason or it could just be his process to allow him to do his job better, he could be slightly overloaded with the areas he's been given and is doing that to make sure he doesn't miss something. Not going to defend it necessarily but whilst he might be being a bit bloody minded it seems you might also being the same in the whole "It's not in the AIP as far as I'm aware so I'm going to call you out on it".