The instructions stated that that piece would need to be sanded as the slider would touch it and once dirt and grime got in there it would squeak. To me I see no real difference between sanding some down and cutting some off. It was a difference I was and am okay with. Like I said, I'll let them know, but not like I'm going to ship them back and wait another 3 or 4 wks for another set when the modification I had to do to the plastic piece wasn't that severe. To each their own though. Some may not be comfortable with that and that's okay too.
Honestly that doesn't really seem acceptable either, why should you have to sand it?