inserting into "date" field returns error (COPY/BINARY)

I have implemented a C++ procedure for inserting data using libpq and COPY
WITH BINARY command. All field types are working as expected in PG9.2,
except "date":
ERROR: incorrect binary data format
CONTEXT: COPY table, line 1, column date_xyz

The passed value for "date" is a 64-bit integer, calculated by the same way
as the value for "timestamp". Should they be different?

Here is simplified fragment of code:
typedef __int64 PGTimeStamp;
...
pField->dataLength = htonl(sizeof(PGTimeStamp));
DBTIMESTAMP ts = { 2012, 10, 5, 0, 0, 0, 0 };
*(PGTimeStamp*)&pField->data = ConvertADOToPG(&ts);
...
PGTimeStamp ConvertADOToPG(DBTIMESTAMP *ts)
{
double date = date2j(ts->year, ts->month, ts->day) -
POSTGRES_EPOCH_JDATE;
double time = time2t(ts->hour, ts->minute, ts->second, ts->fraction);

double tmp = date * SECS_PER_DAY + time;

PGTimeStamp rez;
int* ptmp = (int*)&tmp;
int* prez = (int*)&rez;
prez[0] = htonl(ptmp[1]);
prez[1] = htonl(ptmp[0]);

return rez;
}

I'm definitely missing something, please help.

P.S. Documentation mentions about possible compatibility issues. What are
those?
TY!