If you give yourself resistance with an amplifier or 8 or higher, you actually gain absorption health when you are next hurt. You can gain up to 8 absorption hearts with this bug.

Steps to reproduce:

1. Enter survival mode.
2. /effect @p resistance 99999 8
3. Do something to cause damage to yourself, like teleporting high up into the air and falling.
4. Notice that when you get hurt, you gain absorption hearts.