I have this thing going on here on my rig with Yosemite DP8.
Normally I have two network interfaces active LAN and WiFi on the same network. I have also file sharing active.
My computer name was set to Stefan's iMac initially. Lately though I see that it changes to Stefan's iMac (1), Stefan's iMac (2), Stefan's iMac (3) and so on up until 10 is the highest I've seen so far. An example here:
So one would say: "Sure, you can expect that. You are using two network interfaces at the same time on one network with the same netbios names!"
So the simple test would be to disable one interface and see what will happen, right? And so I went on and disabled LAN as WiFi n is better than 100Mb network cable connection.
Unfortunately I still experience the same behaviour as before. In Finder I see this:
You can see here many versions of it but the hack is the same with only one interface active.
If I try to change it back to Stefan's iMac from Stefan's iMac (whatever number), in couple of second or if I close System Preferences it goes back or changes to some other number.
How do I prevent this from happening? I searched and I can see that people with real Macs have or had this also, but I didn't find a working solution.
Only thing I can think of is flushing you DNS cache...
But this is also a developer preview so don't expect everything to work flawlessly.