Kalista Ult

I was playing earlier with a Brand support who I had linked with. They got caught out by a gank and I tried ulting them. My ult when on cooldown as if it had worked but then they still died. The red orb appeared next to me showing the ult had gone through and even threw itself out as if someone ulted away from the enemy. So because Kalista's ult is bugged my enemy got a free kill