Morgana's Black Shield does not work on Caitlyn's Yordle Snap Trap
's Headshot passive says that her next basic attack against enemies rooted by Yordle Snap Trap is empowered. Rooted is the key word here, only enemies rooted will trigger the passive.
's Black Shield prevents disables during its effect. Root is a type of disable.
The bug occurs when Morgana triggers one of Caitlyn's Yordle Snap Traps while Black Shield is active. At first it seems to work as intended, in the fact that Morgana can walk over Caitlyn's Yordle Snap Trap without being rooted. The bug occurs in the fact that Morgana is still revealed, and Caitlyn's auto attack is empowered.
TL;DR
Since Caitlyn's trap and passive say that her autos are empowered only whilst an enemy is rooted by Yordle Snap Trap, and
's Black Shield prevents disables, root being a disable, Caitlyn's auto's should not empower, and Morgana should not be revealed, yet both happen.
Note: As a Morgana player, this is incredibly confusing and counter-intuitive, in the fact that I will often just pop my Black Shield to get rid of Caitlyn's traps, forgetting that i can still be Headshot from across the map.