I’m having a very similar issue with raytraced translucency. And if I try to combine it wiith translucent shadows or raytraced reflections either of, or through translucent objects things get really weird.
Interestingly, I also do a good bit of work using Maya and the Arnold renderer. Arnold recently began supporting GPU raytracing, and of course it is significantly faster. But, transparent shadows are not working right, so any scene I make that requires that I will switch back to CPU raytracing. So, I’m beginning to think that the problem is actually in the GPU hardware or the OpenGL API.