the block dispense armor event does not fire when an entity is equipped with a chest, donkey for sure, probably others.

nor does the blockdispense event seem to fire.  

@EventHandler
public void onChestDispense(BlockDispenseArmorEvent e)

@EventHandler
public void onChestDispense2(BlockDispenseEvent e) {
System.out.println("Checking dispense 2??");

nether events ever fire if an entity is equipped, if a player is equipped with diamond armor for example the armor event works as expected, if nothing is equipped the regular dispense event works as expected.