Zac not stunned by Crystal Arrow

Not entirely sure if this is a bug, but twice during an ARAM Zac was hit by Ashe's Crystal Arrow ability while he was in the air from his ability and didn't appear to be stunned. Not entirely sure, but maybe he was stunned and perhaps the duration of the stun expired before he landed? Neither was long range arrow, at most maybe 800. Either way, seemed a bit odd, hence this report.