I think the trick is to do another change through the Webconfig to an existing interface and change it back afterwards. This fires of a clearsync event which tidies up a lot of things in the background. There must be other ways for firing off a relevant clearsync event. but I have not really looked for them as I can't read php code. Restarting the server is a bit of a drastic way of firing off a cleasync event.

I've had a vlan tagged connection for a while now, and as Nick reports the config file will be in sysconfig.
I've never had a great deal of success with the web gui, and always did the config from the command line.
After changing anything, I always did a network restart, followed by a firewall restart.
Sorry for the delayed response, was at the Dayton Hamfest - my other "hobby" :-)
Cheers
Paul

btw does anyone it there is any clearos documentation about vlan's. I can't find it...

Okay I searched with:

updatedb&&locate eth0.1003

output:

/var/lib/dhclient/dhclient-eth0.1003.leases

/var/lib/dhclient/eth0.1003.routers

/var/lib/syswatch/eth0.1003

I renamed the files to *.bak and restarted the server. Problem solved!

Thanks Nick I owe you some beers! Personally I don't drink alcohol so if you don't mind I'll take a Cola...

That is the weird part there isn't...

There should be a corresponding ifcfg- file in /etc/sysconfig/network-scripts. You could try deleting it (or moving it elsewhere). You may then have to do a trivial change to either of your other interfaces then change it back to trigger a clearsync event.