microcontroller ROM copy trouble ?

I have a working (ie. tested) microcontroller board uses a
(Philips MAB-8031-AH-12p) MCU a 8051 variant, maybe romless ?
with a (NEC 23256AC) ROM chip.

i removed the ROM chip (NEC D23256AC) and copied it using a ROM
programmer, then i programmed that ROM image onto a (ST M27C256B)
EPROM

i put the new ROM  (ST)   onto the microcontroller board and i

t does **NOT** work ... a no go.
i removed the  ROM (ST) and put the ROM (NEC) back and works like
a charm... no problems

i download ROM images from both (NEC) and (ST) and compare in
file compare program which declares them as exactly the same
?????

HELP please?? any ideas what is going on here.

the only funny thing about the microboard (that i know) is that
the ROM memory socket  has (pin1) tied to (pin 27) that is Addr15
(pin 1) and Addr 14 (pin 27)  ??? do not know why ????

thanks for any help i  am stuck again,
robb