Fiora and Kayle Ultimate Interaction

I don't know if this is a BUG or just broken champion interaction... I picked Fiora in a ranked game and other top picked Kayle. It was horrible. I fed badly. Their e was off cooldown for around 3 seconds in which I could take 2 or 3 cs, or hit one vital. Point is I started to come back and ulted them at level 7. They ulted. You cannot hit vitals while Kayle has a target ulted, and I don't think that is meant to work that way... Fiora's ultimate description says that if Fiora 'hits' all four vitals, and I think Fiora should still be able to break the vital, maybe not deal damage, but if Kayle ults and Fiora uses all her movement (Flash, Q, ect.) she just wasted everything and gained nothing. It doesn't FEEL ok to play with because it doesn't make sense. Fiora is still striking Kayle, she just isn't taking damage. This would make sense if Kayle's ult made her target UNtargetable but when they are invulnerable and Fiora can proc her Q's cooldown reduction on an invurnable target, it REALLY feels like she should be doing something with this.