TLDR: Voltaic Blaze is bugged and will not spread Flame shocks if you turn away during the animation of Voltaic Blaze. Noticed this happening in PvP a lot.
I noticed earlier today when testing out Stormbringer stuff that Voltaic Blaze occassionally would not apply any Flame Shocks to nearby targets, even when they are stacked on top of each other. It was pointed out to me that there is a bug with Voltaic Blaze: If you turn away during the animation, it will do the damage but not spread Flame Shocks
This makes Voltaic Blaze a bit annoying and slightly unreliable unless you pay close attention to the animation and do not face away until its done.