I think I've figured out what is happening!!!!
I will try some more testings, but I think it's a matter of the FONTS!!!, I've installed and used some "Standard" TTF fonts from my PC (Arial and others), and they worked perfectly with TXT eBooks, but seems to be problematic with PRC files.
As soon as I've completely check it, I will post my results.
Bye (Oh!, always writing bad this word...., jjeje)