I used ImageMagick software to convert PNG 32 bit to PNG 16bit (RGBA4444)
This isn’t a bug - as PVRTexTool is a texture tool and not an image tool, the bit depth of image formats not recorded. Image files are simply turned into 32-bit bitmaps and PVRTexTool works from there. This is true of loading any image files into PVRTexTool. To manipulate texture data, PVRTexTool needs the texture to be in RGBA8888 anyway, so nothing is lost.