Morgana Black Shield w/ Vi ult bug

In my last game, on two separate occasions when I was black shielded during the knockup portion of Vi's ultimate, the duration of the knockup was extended due to the black shield cast. The duration was normal when I was not black shielded, and when I was black shielded properly before the knockup I was protected as normal. However, the black shield/knockup bug occurred twice at different times in the game.