I tryed converting this 128*128 RGB TGA in PVR OGLPVRTC4:
And i get this result with the cmd line version:
and this result with the GUI version:
There are little corruptions with or without borders. I dont think it's a compression artifact because it manage to compress very well the cloud gradiant on the rest of the image.
It's not a serious problem, i dont see it on my PC application or on my IPhone, maybe it's just the displaying in PVRTexTool.