[GAMEPLAY] Thresh hooks Illaoi while she's ulting

As Thresh, I hooked an Illaoi as she was doing the jump animation for her ult. After the animation completed, she kept moving without being cc'ed and the chain briefly stayed attached to her before completely dissapearing.

The LoL wiki says:

Illaoi Ult: Illaoi is immune to being displaced while in her cast animation.

Thresh Hook: -Death Sentence is classified as a stun rather than a pull. -While the tether persists, Thresh cannot attack and periodically tugs on the tether, each time pulling the target a short distance toward himself. After 0.5 seconds, or instantly if he hits a minion or monster, Thresh can reactivate the ability to use Death Leap while the tether holds. -The stun will be ignored by targets with crowd control immunity, such as Black Shield. However, the tether is still formed and Thresh can still dash to his target.

I suspect what happened is that the stun connected, but the ult animation proceeded through it. Then, at the first tick of the pull a short time later, the ult animation was still running, so Illaoi couldn't be displaced, so the triggering ability (the thresh hook) was cancelled in its entirety, rather than just the displacement portion being ignored.

I suspect the intended behavior is for the thresh hook to connect, the Illaoi ult to complete, any ticks of the pull that occur during the ult animation to be cancelled, and then the chain stays attached, any remaining pulls work normally, Death Leap is available, and Illaoi remains stunned for the rest of the duration of Death Sentence.

In any case, if the Thresh hook is not applied, I would expect some animation to trigger like it does for a spell shield, rather than the complete disappearance after a short time that I observed.