Simply put, you do damage before the AA animation is completed. This is not the first time this bug has surfaced. Hopefully this gets fixed soon.
I have only played one game so far today with Caitlyn. Will see if the bug persists.
This doesn't seem to be a recurring bug. Just went into a custom and the bug is gone. I wonder if this has to do with a strange interaction with pix as lulu was the support last game and I think someone brought it up that Lulu was a bit glitch'y.
Happens to me when i play caitlyn quite often. Its part of the reason i stopped playing her for a while. Its annoying and kinda screws me up a bit
