Cannot dump/restore text value \N

To be clear, this is not about \N as the default external
representation for NULL, I'm talking about a string consisting of the
two characters backslash and uppercase-N.

CREATE TABLE nonu (tx text NOT NULL);
INSERT INTO nonu VALUES ('\\N');
SELECT * FROM nonu;
COPY nonu TO stdout;

This correctly gives:
\\N

Now try to feed that back into the table:
DELETE FROM nonu;
COPY nonu FROM stdin;
\\N
\.

ERROR: copy: line 1, CopyFrom: Fail to add null value in not null
attribute tx
lost synchronization with server, resetting connection

This happened with 7.3.4, while trying to restore a 1.3 GB dump :-(
ERROR: copy: line 809051, CopyFrom: Fail to add null value in not
null attribute text
FATAL: Socket command type 0 unknown

The bug is still in 7.4Beta3; didn't test with Beta 4 yet.

Servus
Manfred