Excuse me if I'm being dumb, but could this 'hybrid firmware' be created because when you start installing the retail firmware it does actually start installing it, and then when you swap hard drives and start installing the debug firmware it installs a bit of the debug, thereby literally installing a firmware which is half retail and half debug. Also, if this is the case I can't see this being much use in downgrading etc, because you'd just end up with a firmware thats half the latest, half the older one. Of course I'm probably completely wrong...
Well what I'm saying is that downgrading using this method would potentially start installing the latest retail firmware, putting half of that on, then after the swap would finish off by installing the latter half of the older firmware. Thats the only reason I can think of for debug options to be installed but not work, perhaps the hybrid firmware is literally a hodge podge of bits of the retail mixed with bits of the debug.