Yep, I had this periodically with DD1 and now with DD2 (who is 15 mo). At first, I assumed, like you, that it was something they did not like. Later, with DD1, it was just something she did to entertain herself and push the limits with me.
I just started offering food one at a time, or in very small portions until I knew it had been chewed and swallowed before offering another piece.