Oh, I think I understand !
I've made some tests before, and I still have a NAT rule on my Asus router : 80 to 80 (192.168.1.78).
I don't know if it true, but if I don't put port in my URL, as it's HTTP, it listen on 80, right ?
So, if it is, you were right about DMZ, it was interfering with...