Yeah, DS is doing the same thing with BM in the mornings.
He has a feed at 5amish - normally just 1/2 a side which he guzzles, since he's been asleep for 10-11 hours - then goes straight back to sleep.
When I try and feed him again, around about 3 hours later, he's not normally that interested - will have a little, then faff about.
We then get up and have breakfast together (fruit & yoghurt and the like) -doing BLW so it's debatable as to how much is actually eaten.
Then, when I put him down for his first nap at 9amish, he'll normally have 1/2 a feed of BM (1 side) and doesn't want any more.
The rest of the day he still seems pretty normal - happily feeding 3hrly.
It worried me for a couple of days when he first started doing it, but I figured it's just another one of those curve balls that babies throw you when you think you've got them figured out!