COPY command with timestamp and NULLs

I recently upgraded to 7.1.3.  I was experimenting with a script to
export data from FoxPro into an SQL file and multiple data files.  The
SQL file creates the tables, indexes, foreign keys, etc, and calls the
COPY command to load the data from the appropriate data files.

It appears, and I could easily be mistaken, that the COPY command does
not allow NULLs into a timestamp field, even though the field is defined
to accept nulls.  Actually, it appears that the behavior of the COPY
command changed as I believe it would accept nulls in the prior release
7.1.2.

In any case, I'm using the COPY command WITH NULL AS '^N'. And the
datafile contains ^N in timestamp fields that could be NULL, but the
command fails with an invalid timestamp error, referencing the first
line that contains the '^N' null sequence.

Any thoughts?

Thanks,
Dwayne