when adding a second enchantment to armor via anvil second enchantment does not appear on armor

the second enchantment would be added to the armor (iron chest plate)
Describe what you thought should happen here

the first enchantment stood the same and the second one was not added
when i put my iron chest plate with a protection 1 enchantment in a anvil and added a blast protection 2 protection one stood the same and blast was not added to the chest plate

Steps to Reproduce:
1. add protection 1 to a iron chest plate via anvil
2. then add blast protection 2 via anvil to the same iron chest plate
3. take and it should still have protection one only