ahh, it's possible the transmitter (on a remote control) is faulty, even if i press a key just briefly, i'm getting the 'FFFFFFFF' codes - loose button, or 'debouncing' ?
No - that is normal, even with a short press you can get the FFFFFFFF repeat codes.
In most cases just ignore the FFFFFFFF codes in this NEC protocol, unless using VOL+/VOL- or brightness in the case of lights.