The bug
When you get fire and when you jump, you touch it, you will have a jump boost and you can jump over fences (1.5 blocks).
Video demonstrating the issue: https://www.youtube.com/watch?v=FamXf1aV_ZY
Comments 17
@unknown I've made you the reporter of this ticket so that you can change affected versions yourself. Please keep it updated.
I would imagine this is intentional, as fire and other forms of knockback do push you upwards. Though it can be exploited to jump higher, the entire functionality of knockback is to knock you back... I think this is just a side effect of an intended feature.