I'm not sure, but it could be that it's an HI sequence instead of an actual dream. It seems to fit with the characteristic of HI that it's short, fragile, and occurs when between the sleeping and waking states. Also, you don't simply lose lucidity, you actually wake up after this every time! Dreams shouldn't disintergrate that quickly out of themselves like that, but HI does. Also, you don't feel any sort of big transition except for your vision 'blinking over'. It all seems to indicate HI.
I wonder... try this technique again, but don't think of it as a lucid dream but as HI. Try to see more after it fades. Continue it as if it was a WILD. It seems to me you can somehow skip the relaxation step and move quickly into vivid HI, and maybe this can help you to actually achieve a full LD.