@Riot, can I get some context as to the interaction of Annie's Q with Untargetability?

So, I was playing Vladimir against an Annie today and I used my pool to avoid her stun on Q...only to come out of my pool and be stunned by her W, as in the stun was not consumed and her passive stayed stacked. This is quite annoying to me, as I feel that skillful use of abilities should reward you in some way. Instead of feeling rewarded for dodging the stun, I just felt like I was delaying the inevitable. It would be great if this could be changed, but if not, I would at least appreciate some of the reasoning behind why it's like this. Thanks.