Ubuntu :: Playing With Tty And Pty (echo And Cat)?

I've read a bit about pseudo terminal but I still don't get it fully, I've found a really sweet article:

[URL]

I thought the two end tty and pty were acting like a pipe so while testing, I opened two terminals:

terminal1: cat /dev/ptyq9
terminal2: echo "test" > /dev/ttyq9

And it worked, terminal 1 printed: "test". But if the pipe is bi-directionnal ( as terminal were echoed back what user was typing), I was expecting to be able to go the other way around:

terminal1: cat /dev/ttyq9
terminal2: echo "test" > /dev/ptyq9

It does not work ! Echoing on pty just terminates the cat on pty. How is the "return" working them ?