Right clicking armor when you already have armor equipped in the required slot does not drop/swap the old armor or equip the new armor.

The new armor is not equipped, it remains in your inventory. The old armor is not swap/dropped, it remains on your character.

Steps to Reproduce:
1. Right click a piece of armor (Example an Iron Chestplate)
2. You equip the armor!
3. Scroll to another piece of armor for the same slot (Example Gold Chestplate, Diamond Chestplate, Another Iron Chestplate, Chainmail Chestplate, or Leather Tunic)
4. Right click the other piece of armor
5. Nothing happens!