Why is the PHP ipc message not in the queue?

Why is the PHP ipc message not in the queue?

In PHP I try to send a message through IPC, and to immediately check if
the message is in the queue. Here is a test code:
$rQueue = msg_get_queue(12345, 0660);
msg_send($rQueue, 0, "test", FALSE, FALSE);
print_r(msg_stat_queue($rQueue));
which prints out the statistics from the given queue, indicating
msg_qnum=0, i.e. no messages in the queue. I expect at least one message
in the queue instead. Where is the problem?