[Gameplay, Major] Doran's Shield's damage reduction does not work properly vs. spells.

After some preliminary testing with a friend of mine, we found that the damage reduction passive on Doran's Shield is not working properly vs. spells. Sometimes, it doesn't reduce damage. Sometimes, it does reduce damage, but not as much as stated. Sometimes, it even increases damage.

We tested with 6 different champions, and we found for each:

Xerath: Does not work. Syndra: Does not work. Ryze: Does not work. Annie: Does not reduce by 8 damage like the tooltip says---instead reduces by 6 damage on her Q and W. Anivia: Does not work. Vladimir: Does more damage vs. champions with Doran's Shield in their inventory (+6 on Q, +2/tick on W)

Reproduction steps:

1. Pick any champion.
2. Go to lane without Doran's Shield. Level up to 2 or 3.
3. Go to baron pit (to make sure minions don't aggro on you and mess up testing), and hit your punching bag with spells. Record the damage numbers.
4. Buy Doran's Shield and repeat #3.
5. Note that the numbers aren't reduced properly.

Reproduction rate: 100%

Server: NA

Thanks in advance to any Rioter that takes the time to read this.