I've seen this comment a few times now but fail to understand it. Why is it recommended not to walk around the aircraft to stretch your legs? You don't have a Post-It attached to your forehead proclaiming which cabin you are travelling in (unless you are being deliberately obnoxious), so do the crew really think there will be a riot if a passenger passes through a curtain while taking a walk? Doesn't say much for how your average Y passenger is thought of if the inference is that they would react poorly at the mere sight of someone from another cabin passing through...

I must be missing something.