Bugfix #25301

Preview render for node shaders broke, caused by localizing 
materials last week, to prevent thread crashes. Fixed now.
Also added a temp fix to draw color-management corrected
node previews default. Will follow scene setting tomorrow.

Also: SSS in nodes doesn't render yet. Was issue in 2.4 too...

source/blender/render/intern/source/pipeline.c

@@ -2050,7 +2050,7 @@ static void load_backbuffer(Render *re)
 		char name[256];
 		
 		strcpy(name, re->r.backbuf);
-		BLI_path_abs(name, G.main->name);
+		BLI_path_abs(name, re->main->name);
 		BLI_path_frame(name, re->r.cfra, 0);
 		
 		if(re->backbuf) {