Braum Passive Bug

Recently I was playing a game as support Braum with Ashe in lane with me. We chased an enemy up the river who had 3 stacks of concussive blows on him. Ashe shot an auto attack at him, but while the arrow was mid-flight, the three stacks timed out. When the auto attack hit, it reapplied the first stack of concussive blows, something that only Braum is supposed to be able to do with an auto attack or Q. Has anyone else seen this bug?