Volibear Q interaction with Morgana's Black Shield

So, I played a game as Volibear against a Morgana. The ADC was really low, but had Morgana's shield on them, and I used Q for the movement speed to catch them (I knew the flip wouldn't work). However, instead of simply negating the flip, the entire autoattack was negated - no damage, no titanic hydra proc, and most importantly, the Q buff was not consumed - which meant the next autoattack was also an attempt to flip the ADC behind me. Which meant it was completely negated as well. Which meant a Caitlyn with about 10% HP was able to kill a Voli at about 30% HP, when the Voli was already in melee range. Is this the intended behavior? Because I feel like it can't possibly be how this is meant to work.