Wrong length of bytea field

I inserted two binary files to a bytea field "contents"

file1  size was 7834649 bytes
file2 size was 5888534 bytes

select filename,
octet_length(contents),
length(contents)
from localfil

returns

"file1                              ";16777184;16777184
"file2                              ";15768893;15768893

It seems that for some reason postgres returns sometimes escaped string size
(eq. single byte 0x00 uploaded as \\000 size is returned as 5 )

Why result is incorrect ?
How to get the actual size of bytea field ?

Using Postgres 8.1 in XP , cluster encoding is UTF-8

Andrus.