Armor Stands created before version 1.9 will have their items be in the wrong slots/deleted upon world upgrade.

Reproduction Steps

• Create a world in 1.8.9
• Place an armor stand
• Give it arms with /entitydata @e[r=5] {ShowArms:1}
• Give it full armor and place an item in its hands

• Use this world where steps 1-4 are already done : MC-264319.zip
• Load the world in the latest release

Observed Results

• The armor stand now holds its boots and leggins in its hands (regardless of if the armor stand had arms before)
• The item it had in hand is now in the boots slot
• The helmet and chestplate are deleted
  
  
  Expected Results
• The armor stand would be upgraded properly