I'm not quit sure myself, but I can offer what little knowledge I do have! Bettas do often spit out there food once or twice if the flakes (or food item) is to large for them to swallow whole. Its a form of chewing, or so I've been told? I don't think its abnormal for the betta to do this sort of behavior.
Although! It may also depend on where you got the betta fromm, and what they were feeding to it. For example, breeders might choose live bait over anything else, and so if you had purchased the betta from that breeder, it may just be adjusting to its new food source? <--- This is just a theory, although I couldn't see why it -wouldn't- make sense.
On a side note, my betta also did this at first with both his BettaMin flakes and freeze dried blood worms. Now I crush the BettaMin to as tiny as possible without it become dust... <.<; lol It seems to work out. also, I've recently been pre-soaking the freeze dried blood worms in a cup of his tank water, to soften it up for him.
Until a more experience response appears, I hope this helps! ^_^