Draven and Rapid Firecannon

Not sure if this is 100% a real bug or if i just misunderstood my situation, but I build rapid firecannon on draven. I attacked with a spinning axe and while it was returning to me in the air my normal auto attack generated my 100 stacks with the item. Upon catching my spinning axe I lost the 100 stack charge from the item. I only noticed it once but wanted to report it regardless