How to reproduce

1. In a creative world, place down a repeating command block and then type "/item replace entity @p armor.head with minecraft:air"; then run it so that it continually repeats. (you might want to turn of commandBlockOutput)
2. Wear a turtle shell. The item will be deleted as expected, but the potion icon will flicker until it reaches 0. It will then be stuck at 0 until you relog or go to the nether.