Our theory is that Gmail does not like "duplicate" messages. Because there is a copy of this message already in your "Sent" folder, it appears that gmail will ignore the copy that has made the round trip through our server and back.
If you try your test from some other Gmail account (one other than the one the message will ultimately be delivered to) then it should arrive normally.
Gmail also filters spam and viruses fairly vigorously, and sometimes test messages blend in, so don't forget to check your "Junk" folder if you're expecting a message that hasn't arrived. We also have some reported cases that messages sent to Gmail sometimes simply don't arrive (whether forwarded through our system or not).