The Bug:
Swapping armor by right clicking with an item deletes the old one you had equipped.
Steps to Reproduce:
Equip any armor.
Hold any equivilent armor type (that you can swap with the equipped one) in your hand.
Use it in survival mode.
Observed Behavior:
The old armor piece you had equipped gets deleted and replaced with the new one.
Expected Behavior:
The old armor piece should swap with the new one.
Linked issues
Comments

Thank you for your report!
We're tracking this issue in MC-275755, so this ticket is being resolved and linked as a duplicate.
That ticket has already been resolved as Fixed. Please check the Fix Version/s field in that ticket to see in which version this behavior was or will be fixed.
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Duplicates MC-275755