Annie Disintegrate Disappears!

I have been playing Annie for quite some time now and this little bug has been annoying me! This has happened to me 5 times now...

My Disintegrate on Annie completely vanishes when I need it! I have never been able to catch it on a recording until the new replay system was introduced (ty Rito, I really love it!) From my understanding of the bug it seems to only happen when you are on 4 stacks on Annie's Pyromania passive. When you go to Disintegrate Stun the enemy and they have just activated a shield or has a shield ability or used a shield ability recently Annie's Disintegrate ability will disappear! The stun will not go off and not use any charge of the passive however the ability will still go on cool down!

The other champions I have encountered this interaction with are; Viktor, Orianna, Lulu, Karma and Yasuo (and I am 100% sure his windwall was down!!!) Please fix this annoying bug cause when it happened verses the Karma it cost me a Ranked game! Luckily it was not a big deal verses this Ryze but it was still very annoying!

Thank you for your time!