Sometimes when getting knocked back by a monster, mostly Rogres in my experience, you slide along the ground until you either collide with a wall or fall off a cliff. I just got slammed and ‘flew’ about 120 metres.
Not a bug. This behaviour was discussed here not long ago, and IIRC the devs answered something like: “its core game physics, we don’t know how to change it, so relax and enjoy - it’s here to stay”
It happens a lot if you jump at the wrong time during some boss attacks, typing from experience 
It’s 2021 and I’m still mad at players losing all weight while jumping. The slightest touch of a slave rat sends you off the nearest cliff
Not (easily) fixable doesn’t mean not a bug 
It is in devspeak! Called a feature. 