With 3 production lines each generating 12 balloons/tick, buffed to 16 with the Petite Party Cake, I only received 36 balloons, implying either only two lines are producing or the buff isn't working. I'll try and catch a screenshot next time, but it sounds as though this is a problem others are having as well.
Quick addition: I do have two lines producing with the same input. Not sure if that's relevant. Iron swords/Iron swords/Steel swords.