Item Quicksilver doesn't prevent the displacement from Gnar's Ult.
I'm pretty sure it blocks the stun which follows the displacement and Item's shield does proc and goes on cooldown. So it seems that only displacement part of Ult is bugged in that interaction.
You can't QSS to get out of displacements. You can QSS then flash out though. With Gnar it's either best to flash his R, or take his R then QSS and then flash if you have to. If you try to QSS->flash out of the displacement you might not get your flash off and get stunned
Lee Sin's Dragon's Rage (Lee Sin R) roots you for 0.25 seconds and then kicks you. You can 
or self cast 
the root and flash the kick, you have to be very quick though https://youtu.be/x1rjjEOpusY?t=16. Not too many people know that self cast crucible will "cleanse" roots. You can't self cast crucible during cc where you can't use abilities though
Can confirm that it doesn't work, the broken interaction just lost me a game. [slayer-jinx-unamused]
