He might be looking for that extra special something that he gets at night. How about saving some of last night's left overs for the morning feedings as well? Pasta is good, or well i add in low fat cottage cheese, or canned pumpkin, or canned no salt green beans, or sardines to my own pooch's meal. Just little things to keep things all jazzed up and interesting.
He may also not like his food.. which could also be why he's reluctant to eat it in the morning, but will gobble it down when he's really hungry later. What do you feed him? It may also be why he's not filling out correctly...
Good Luck.