[Stiglr]

No, it's that the render engine for AC3D is just not the best. Sometimes, when you zoom WAY in, you'll see surface selection colors appear and disappear, as the renderer undergoes "z-fighting"; it's trying to "decide" whether to display the selection color or not, or which layer has display priority; especially on thin, two-sided objects where one side is selected and the other is not.

When your 3D surfaces have problems that actually affect the integrity of the model, you'll see red or blue lines along the surface borders. Those are the "real" problems!

In that screen grab, I see no apparent problems.