Losing Sorcerer 6 buff when some sorcerers die.

Hi! I just played Void 3 Sorcerer 6, so I could see my Cho'gath's ult damage with precision. I had a lvl 2 Cho'gath, meaning his ult does 500 true damage, 1000 true damage with Sorcerer 6 buff. Which he did... most of the time. However, sometimes, when some of my sorcerers die, suddenly his ult only did 500 damage. I don't think this is inteded behaviour, so I think it might need a fix. Thanks!