I see this ALL the time. It's not that folks are purposefully disrespectful, I think they just do not realize that they are actually turning their back to the Altar.
I feel very awkward when I refuse to turn backwards, and end up being one of the remaining few facing forward...with everyone in front of me facing ME. You know? I don't know where to look. Instead of seeing their backs, all of a sudden I see all their faces..and I self consciously end up looking at the floor or my hands.
This happens not only during censing, but, anytime anything happens towards the back of the church.
During the blessing of the water on Theophany most everyone turns their back to the Altar to watch the water getting blessed in the back.
Just last week during the Pan-Orthodox Vespers on Sunday of Orthodoxy, everyone turned their backs again, as the priests made their way with icons around the sanctuary.