Our lo went on 3 hour EASY at 7 weeks and 4 hour about 5 weeks ago. The reason I went to 4 hours was because he was doing what yours was - bopping off and on and grinning and talking to me. Alas, after a few weeks on 4 hours, he was doing the same thing after only 10 or 12 minutes! I realized, just as Carter's Mama suggested, that he is just eating more efficiently!
Right around starting 4 hour EASY, his naps went down the tubes for a while. I just persisted with trying to extend them and trying to keep him up a little longer for A time and finally over the past 3 days he is able to go to sleep easily again and transition through on his own to have a longer nap. We went through about 4 weeks in all of April with him waking about 45 minutes into his night time sleep and I'm sure it was due to the crummy naps as well. As soon as his naps started to improve, this started to stop. He still makes noise once in a while after 45 min but if we leave him he'll resettle himself within a few minutes.
We're now battling night time wakings! He wakes 2 times needing to go back with out eating and 1-2 times starving for a feed. I'm thinking he may be ready for a bit of cereal -he's a big boy, too - was 7lbs 14 oz at birth and 14lbs at the beginning of March. He has his 4.5 month appointment tomorrow and I'm sure he's close to 17lbs now!