Normally after defeating the Ender Dragon, it will disappear and experience will “burst” out of it. However with this glitch, the experience falls straight down entering the portal if it is not blocked and there will be significantly less experience than usual. To reproduce the glitch, simply defeat the Ender Dragon. 

Edit: I apologize for the poor quality, this was recorded straight from my tablet. This was also done in Creative however Survival also has this problem.