If you're trying to use non power-of-two textures on a PowerVR based device, and you're confused about why it refuses to render them half the time, there is indeed logic behind it. PowerVRs will only render an NPOT texture if you don't have tiling enabled. Break out CLAMP_TO_EDGE and all will be well.
We'd primarily been testing on a Tegra at the time this came up, and it took a while before we realized what was going on. Hopefully this note saves somebody some headache in the future!