League-of-legends – Do Caitlyn’s Traps still reveal stealthed targets

Stealth can only be broken by a stealthed champion performing an action that breaks stealth.

Though not viable by any means, before the sunfire cape's damage was a unique passive, it was fully possible to simply buy multiple capes and follow an enemy champion around while stealthed, relying on the damage to slowly kill them.

In this case, Time Bomb reacts the same as if you cast it on a ward - because the target is stealthed, the effect won't be visible, nor will it break stealth upon detonation. The enemy would just get a sudden burst of damage with no apparent cause.

After some rigorous testing with my friend Zamual05, we've managed to determine that Pix does not intercept Caitlyn's ultimate.

We tried two different variations, to include Lulu running away (placing Pix behind her, in direct line of the shot), and Lulu standing still; in both attempts, Lulu took the damage directly with no interception from Pix.

In conclusion, no. Pix should not intercept Caitlyn's ultimate. What you experienced is definitely a bug.