Steps to reproduce:
1. Download attached project
2. Build and run it on WP8.1
3. Change orientation while app is running. Render Texture will show artifacts until it is redrawn by visual content update in it.

Why is this not going to be fixed?
This graphical bug happens only when all conditions are met:
* Scene is rendered to a render texture;
* Camera view frustrum is empty;
* Render texture has anti aliasing enabled;
* Phone has Adreno 225 GPU.

It is a driver bug - working around it is possible but that would introduce a performance penalty. Meeting all of the above conditions is not really realistic for a real game, there a workaround will not be implemented.

Furthermore, it's pretty simple to workaround - just add an empty skybox on the camera.