When Lux gets cc'ed as being ulted her ults still channels through and does dmg. With Malz being suppressed, being knocked up or stunned her ult still goes through. It is very easy to reproduce. Have Lux ult and then cc her in any time while her ult is still channeling you can see the process of the cc still going but take no effect.
Her ult is NOT channeled, once it is cast it does an animation and has a small "cast time" but it won't stop it from going off. That is like CCing her mid Q throw, the q is already thrown and still going to travel. Or ezreal arcance shift, Blitz crank pull hits him but he channeled his arcane shift before it so when it hits he is now teleported away instead.
You can't cancel a Lux ult. It's not a bug.
