Auto-change in network name? WTF?! Help?!

It happens to me too and I don't like it either.

Auto-change computer name

If a computer detects that its computer name as set in the Sharing pane is already in use with a different IP number, it is possible that the name of the computer is changed automatically by adding a number between brackets.

Auto-change of the computer name as set in the Sharing pane is already possible if the same computer is connected to the local network as well via wired Ethernet as via wireless.

Auto-change of the computer name as set in the Sharing pane is required if at the same time a different computer is connected to the network with the same name but with a different IP number, that could be a clone, or just another computer with the same name set.

Maybe other computers in the network remember a former combination of a computer name and an IP number.
Maybe it's possible to avoid that the name under Sharing is changed unnoticed by locking the system preferences.

I think this happens because your router still has your computer cached and when you reboot, your computer tries to login again.

I don't know, but it might help if you assign a static IP to your computer

No, a static IP doesn't help. On the router the lease time for IP numbers is set forever.
The iMac has a double connection: wired and wireless. On the router they keep both the same computer name and different IP numbers.
After a restart the computer name is automatically changed by adding (2). That would be correct if the name was only changed for the used IP. But the change concerns both IP numbers. Then I can by hand restore the original computer name. That concerns both IP numbers too.
It would be better if in this case the computer name was not changed automatically or that there was a warning that the computer name would be changed if not one of the connections would be disconnected before.
Is it normal that the auto-change of the computer name is carried out without a warning?

I've had the same or a similar issue. My computer was constantly renaming itself with a (2) every time it booted, after a system lockup. I tracked the issue down to CD/DVD sharing... when turned off the problem went away.

When CD/DVD sharing was on, I could not change the name back to the original version, it would get rejected and immediately set back to the version with "(2)", displaying the message:

+The name of your computer "Name" is already in use on this network. The name has been changed to "Name (2)" automatically.+

With CD/DVD sharing turned off, I could name my computer whatever I liked, even back to the original name. Turning DVD/CD sharing back on again would instantly rename my Mac. It's very persistent bug!

Fortunately I found a fix. I was able to get rid of the problem by toggling Bonjour, as described here:

http://tech.karbassi.com/2007/11/06/leopard-turn-off-bonjour-mdnsresponder/

To turn Bonjour off:

sudo launchctl unload -w /System/Library/LaunchDaemons/com.apple.mDNSResponder.plist

To turn it back on:

sudo launchctl load -w /System/Library/LaunchDaemons/com.apple.mDNSResponder.plist

Toggling Bonjour (mDNSResponder) forced a reset of something on my system somewhere, and now I no longer see the issue on reboot, even with CD/DVD sharing turned on. I can turn sharing on and off at will, and my computer is never renamed. Success!

I don't think this problem has to do with CD/DVD sharing specifically... I think it's a bug in Bonjour. I've seen threads where people have complained about this issue because of printer sharing, or remote management! My guess is that a crash can cause a mDNSResponder config corruption, tricking Bonjour to share devices or services using the same name as your computer, forcing the name conflict.

In any case, I hope this fix works for you too. I know I'm a lot happier now that there isn't a lingering issue on my box!

I think you are barking up the wrong tree. The problem happens when you connect to the same network with Ethernet AND Airport. I think it also has to do with using DHCP on a large network. Bonjour sees itself on the other adapter and thinks it is another machine. It didn't used to behave this way, but now it does.

I believe what is happening is that if there is a delay in getting a lease, and Bonjour finishes registering itself on the network, then the other adapter comes online because it finally got it's lease, it thinks there is a conflict and renames the computer. I get this all the time. I use Spiceworks to scan our network, and because both the name AND the IP address have changes, Spiceworks thinks it has found a new device.

Has you ever cloned your Mac and dumped the image on a different Mac on your network?