
Are any of the inputs to the chip coming from TTL?  Standby-drain specs
for CMOS chips typically apply only if inputs are pulled all the way down
to zero or all the way up to Vcc.  TTL isn't good at doing the former and
it won't do the latter at all without help from pullup resistors.  This
sort of thing can easily multiply power consumption by a considerable
factor, because the CMOS transistors that are supposed to be OFF aren't
all the way hard OFF.