Our dog Atlas is currently 10 months old. He is best described as well trained but very stubborn. Say for example there is something on the counter than he wants, he'll jump at it. We'll say "down" and give him a good squirt with the water bottle and he goes down, then 5 seconds later he is jumping at it again.
I've talked to some animal trainers and they say this kind of stubborn behavior is very common at this age (hence why so many animals at the shelter are young, what was cute as a puppy isn't cute when the dog looks like an adult).
About what age did your corgi end his/her stubborn youth stage?