Lissandra ult bug? (Gameplay)

Today, while I was playing Lissandra mid and top, I noticed that I was obviously getting killed while I was in my ult. One instant was so blatantly obvious to me. I was running from a sivir leo combo and siv through q and i panicked and hit my ult on myself. The ult was cast and I was shrouded in ice but sivir's q still did damage to me on the way through and the way back and killed me. It happened again in that same game at a later point while we were team fighting against their zed. I ulted myself and still got torn apart, not even one second of invincibility was granted.