World says EnderDragon has been killed already

Whenever I attempt to respawn the Ender Dragon for the sake of allowing other people on my server to acquire a dragon egg. Even though I respawn the dragon, then set the "PreviouslyKilled" Tag in the level.dat file to 0 which should allow the death of the Ender Dragon to drop a new egg. The console always states "Found that the dragon has been killed in this world already.", then the next time I check, the "PreviouslyKilled" tag has been set back to 1. Therefore, I cannot do anything for the sake of my server. If its not pulling this data from the level.dat file, where is it getting this information from?