Cassiopeia can ult herself out of Malzahar's ultimate

As I was laning against a Cassiopeia today as Malzahar, the same thing happened twice: As I already casted my ultimate on the enemy Cassiopeia, her ult would fire and stun me, and my ultimate goes on cooldown.

In the first case, she ate a bounce from my e and she was already low so I flash ulted her, but instead, her ult fired, my ultimate went on cooldown and I died. Now how can she interrupt my ultimate if it's an instant supression (and she's the one being supressed)? If you're supressed you can't ult, so you can't un-supress yourself...you know what I mean.

You might argue about cast times here, I'm aware of that. But in the second case my jungler and I both witnessed that when he came to gank, the purple tether was already animated, therefore my ultimate was already chanelling and the same thing happened again (except I didn't die and we got the kill, but it was close).

Is this intended or simply a glitch? Whatever is the case, I don't appreciate it happening. If Malzahar's tether doesn't apply instantly now, than it very well should.

To recreate this simply try ulting with both champions within a small timeframe. It happened twice in the same game, so it mustn't be too hard to reproduce.

Thank you for looking into this.