This appears to happen to me under certain crowd control conditions. Bepop's hook and Abram stuns seem to have a high trigger rate. It may have something to do with the movement applied by their abilities (drag / push) breaking Haze's ult's movement ceiling? I have experienced it being tossed up...
I have experienced the same thing.
It seemed to occur for me when I used Haze's ult under CC effects. I have had it happen when Bebop hooks, Abram stuns -- I suspect here Haze was in Mirage's twister? It may have something to do with spamming the ult key when under crowd control?