Interesting, I'm actually suprised that works at all and I must admit, this one I'm not sure how to fix. In real life, I've always understood that a hard mitre on a corner that's also sloped is pretty much impossible if you also want to keep the profile vertical. That's why on stairs you'll often see handrail sections like this:
In that way, you go around the corner flat before starting the slope again. Of course when projecting onto a surface you can't easily do that. Another option is a smooth deformation like this
This one can be achieved in RailClone using the Fillet Corners option, but that won't create the kinds of corners you're after.
I'm going to have to think about this one a bit, please bear with me.
Best.
Paul