Morgana shield vs Zoe Drowsy -> Sleep
When Zoe first came out, I distinctly remember that if you used Morgana Black Shield after getting hit by Zoe Sleepy Trouble Bubble, but before the Sleep kicked in, you still got put to Sleep. Even someone on the Riot balance team defended this interaction. I know later they slightly changed how Drowsy worked, in that you could Cleanse it and not go to sleep, but the Morgana shield interaction remained the same.
It now works differently. If you shield after getting hit by the bubble, but before the sleep timing, you (properly?) are immune to the sleep.
When did this change?