Karthus Spectral Form Bug

http://puu.sh/tmmIK/d2fdf37178.jpg http://puu.sh/tmmPX/94a2621e8a.jpg

So, I was playing a game recently as Karthus and I noticed in a particularly clustered team fight that it seemed to me that my Death Passive form bugged out for a moment. In the first picture you can see that I look to be in or going into spectral form (Note, I run some spell vamp runes that give me back some health in the passive, which is why I am at almost half HP, weird interaction, I know.) yet by the second picture I am back alive. I feel like there may have been some sort of weird interaction with Kled and his death/invulnerability frames, because at the time, he and I 'died' roughly at the same time. I reserve the right to be wrong, but I have played a fair bit of Karthus and it certainly FELT like I was in spectral form, no movement, slightly different Q animation, auto-triggered Defile, etc. It almost seemed like I went into my death passive for a similar duration as Kled's invulnerability frames, and then came back to life once the duration was over. This is pure conjecture on my part, but going back through the replay in .25x speed, it even looked weird looking back. Anyway, thank for taking a look, let me know if you need any more information.