Killing Spree has been killing rogues since 2008. While assassination rogues are discussing the best opportunities to use Vendetta and subtlety rogues are planning their Shadow Dances, combat rogues are just hoping their cooldown won't throw them off a cliff or into fire. I remember when rogues simply didn't play combat when fighting Magmaw. Killing Spree on Garalon? Only if you had a death wish.
The Glyph of Killing Spree fixed most of these errant deaths, but didn't fix the root problem: Killing Spree takes away control from the rogue. We're not capable of choosing our targets or our destination when using Killing Spree, which makes it a liability in high-stakes situations. The new PTR version of Killing Spree looks to change that. The normal Killing Spree will turn into a powerful nuke on a specific target, while Killing Spree under Blade Flurry's influence will result in the random attacks we're used to.