question about "write " in bash

[Lestat V <dreameration@gmail.com>]

It seems that there is problem with my "write " . The "write"
delivered the message I sent to myself while actually I sent it to
another user. The details is like this:
 After I typed in" echo 'a message'|write USER1", I just got this 'a
message' on my another gnome-terminal. In order to find out what 's
wrong with the system, I typed "w" to get the login users list, and I
got something like the following:
       ME   tty1 ............
       ME   pts/0  ........
       USER1 pts/1 ....

In another time, the "write "even told me that USER1 logined more than
one terminal, while the "w" output indicated that USER1 logined only
one teminal.

Could some kind guy help me to find out what the problem is ? THANX!