PQgetlength vs. octet_length()

Hello everyone.
Having a weird issue.

I have a value inserted into a bytea column, which is about 137megs in size.

If I use octet_length() to check the size of the column for this specific
row I get this:
TestDB=# SELECT octet_length(rawdata) FROM LargeData;
octet_length
--------------
143721188

When fetching the row through the C API, and I use PQgetlength() on the
column of the row in question I get:
(gdb) p (int)PQgetlength(result, rowIndex, i)
$3 = 544453159

I am wondering if I am lacking knowledge that explains why these values are
different, or if something fishy is going on.

What led me to investigating this is that fetching this row in a C
application is causing a failure. My programs memory usage balloons to 1.3
gigs after executing this:
const char *valC = PQgetvalue(result, rowIndex, i);

Am I doing something wrong, or is there some ideas what I should investigate
next?
This seems quite puzzling to me.

Thanks in advance for any help/insight offered,
Michael.