That first save is from a brand new game before picking the starter. I have now advanced to getting the pokedex. I extracted the save again and it seems to be doing the same thing, unreadable by pkhex.
My concern is making a lot of progress on this cart and never having the ability to truly back it up in case something happens.
Attached is the further progressed save. Does it look any different in terms of those blocks?
POKEMON FIRE_BPRE.sav