Nunu Slow hits even if your not near him

Just played a game against Nunu i was playing Morgana i notest when Nunu shot his Ice Blast ( slow ) even if i flashed out of the way of it disappeared and then a few seconds later i would be slowed even with Morgana's Black Shield dont know if that is a bug or something with the champ reading on his info and videos it shows it actually hitting the champ not disappearing and then slowing