Pushed end crystal doesn't summon ender dragon

When an end crystal is pushed onto the bedrock with a piston, granted there is already 3 other crystals placed, the dragon is not summoned. 

 

1. Place 3 end crystals on the main end portal
2. place a 4th end crystal on obsidian one block away from the main end portal
3. break the obsidian to remove the fire
4. push the end crystal onto the bedrock so that it catches on fire
5. the dragon is not summoned because the game hasn’t realized a new end crystal has been put upon the bedrock