What mesh are you using for that spherical model? Was it imported or is that soemthing generated and modified in Ps?
Removing backfaces is only at the rendering level of the Ps Scene; it doesn't remove triangles from the paint engine targeting. If you don't want to paint on triangles, try selecting an area you don't want painted then going to 3D> Show/Hide Polygons>
I tried to mimic your sphere test with the sphere mesh provided in Ps and I can't paint on the backside as you're showing. Ps will paint and render the diffuse material on both front and backside of the targeted triangles, but what your movie shows is an odd UV mapping, as brenBot notes.
Thanks for the video illustration. I see what you're talking about now. That video is using Ps CS4 and we've changed 3D interaction quite a bit over the versions. What version do you currently have, and on what platform do you run?
I have noted a change in behavior with Ps CC and Ps CS6 from earlier versions in this regard (painting with backfaces hidden). I'm doing more background research and will log a bug for further investigation. As a workaround, you might try looking at the 3D> Show/Hide Polygons> commands to remove targets from you're painting.