virtualmin: Subdomain be hosted on another lan server but use same external IP.

First, I would like to thank the community here… your answers and tutorial has really helped me in the past year. Maybe someday i would be able to pay the favor back. A heartfelt Thank you. I have this weird problem. I have two servers, lan addresses 192.168.1.10 and 192.168.1.11 . i have set up webmin/virtualmin on 192.168.1.10. I have forward port 80,53,587,465,143 on my router to point to 192.168.1.10. The main domain example.com is hosted in 192.168.1.10, it works fine. I added a subdomain users.example.com to example.com in 192.168.1.10 then i modified the DNS A record of users.example.com to point to 192.168.1.11 instead of my external IP. Here is the weird part. If i am in the lan network (my computer address is 192.168.1.12) i can surf both example.com and users.example.com very well with no problem. But if am at home i can only surf example.com ,** users.example.com** says no response. What am i missing,Dint the DNS Propagate? i need both example.com and users.example.com to have the same external IP but users.example.com to be load from 192.168.1.11 . How can i achieve this? I couldn’t figure this out since last November! any help i would greatly appreciate.