Ender Dragon dissapears

I go fight the ender dragon on normal difficulty...

I get killed by the dragon, I go back to fight it again, and the dragon's gone and it just gives me access to the portal to get back to the main world. 

This kinda sucks. I wanted to beat the dragon, but it's a bit anti-climactic if I have to go through all that buildup and only get one chance. Can that be fixed?