Ender Dragon Mega-Bug !!

There is a bug that when I am fighting with the Ender Dragon suddenly I see that the portal is activated as if I had already defeated it, this way from nothing! The same thing happens when I die and go back into the Ender Portal, the portal of the center activates when I have not even defeated it. The truth is a pretty unpleasant bug and ruined my survival world, they must fix it!