either the imager is so insensitive to far IR wavelengths that the low number of photons striking it not registered correctly, causing an inconsistent activation of its elements and a resulting effective loss in resolution, or the IR filter that moves into place behind the lens is of such low quality that it introduces the blurriness (kind of equivalent to smearing something like vaseline on the lens surface). I'm inclined to think it is probably an imager sensitivity issue, since it seems like all black flash cameras have the problem (to somewhat differing degrees). The problem is that an imager optimized for low intensity IR light is not going to give good color daylight pictures.