Network accounts, how-to prevent theses changing to Local?

Hi,

I'm running a Mac mini 2011 with ML server 10.8.2 as a home server. I'm using most services Web, Mail, VPN, Calendar, Contact, OD, etc. So far so good, everything works as expected. Basically it is setup like a SOHO server execpt the home part where I need a loggued on account with iTunes running for Home Sharing. This is where I have an issue.

As soon as I log with my personal user (Network type) directely on the mini where my iTunes library physically resides , this user become automatically a local user. I can view it is no longer in the Network users list in Server.app but in Local Users one. The problem is once my user type has changed, I can't log anymore to Calendar, Contact and VPN servers from my iDevices nor my MBP. Thoses 3 will give me error message as soon as they try to log to the server.

And if I log out from this account on the mini, it reverts back to its previous Network type status and everything works again.

So is there a way to prevent this changing behavior with Network Accounts? I really need to have this users logged in or I can't share my iTunes Library anymore.