Fair enough. Well, the only thing I can think of is this:
In this thread, Svr and JustinFan discuss their Rend/WW findings. At one point, JF says:
Maybe in some instances, if your APS is scaling up with every hit, as with Gogok, the instances of Rend are being overridden before they can deal damage, because they are pegged to an AS with, say, only 1 Gogok stack, and the next WW hit occurs a little faster, with 2 Gogok stacks, etc, etc, until you reach the max 15 stacks. So, perhaps when the RG spawned, your Gogok dropped off, and then as it stacked up, your rends were being overridden.
I dunno. That’s my best guess. I’ll keep an eye out and an ear to the ground for any further info.
Edit: just did a little test and was unable to duplicate your results… if you see it happening in the future, try to record video.