In the Education Edition worlds a player who is not op takes fall damage continuously after being granted May_fly ability. 

If you are on a local game the visual effects can be seen. The player who is not OP will bounce up to where they are on their client side, then fall and take damage, The player flying sees no such drop.

If you grant OP to the player they no longer fall and take damage, If you then remove op the player will still fly properly and will not take damage until the next life.