User blog comment:Darksusanoo/(Champion Rework) Syndra, the Dark Sovereign/@comment-1330314-20150728224700/@comment-1920550-20150729003713

Because the innate spheres only count for the first ultimate cast. If that kills the target, she gets the 15 second recast window which will visually be marked by a lack of Dark Spheres floating around her for that time, so there's no visual confusion about the Spheres. After that window of time is over, the passive spheres will re-appear around her.