This is just a theory but if you are using game centre linking on a device where you have an older version of game centre, the one with the green craps table stop!
The version in IOS 8 is different, it has a white background. My guess is that the older version isn't 100% compatible with this new feature since it is a much older version.
I lost the original account on an iPad first gen when I linked another account to this device, it seems the new account may have permanently over written the original account data which up till now was a hidden file on your device and why when you delete the app you could always get your old account back most times.
Once the original account is over written game centre nukes it from it's list so you cannot recover it! Why experimenting with creating multiple accounts on one device is likely a fatal mistake.
Now what I am not 100% sure about is if this is limited to IOS 5 or it will happen to IOS 6 game centres since they also have the older looking app. But my gut feeling is if you want to try linking and running a different account on your IOS device only do it from the game centre in IOS 8, I have not tested IOS 7. But if you have a version of the game centre whose background is the gren craps table I would not try it!
You seem to able to link your accounts fine in IOS 6 but I would not try logging out of the original account and into a different one linked to your game centre account untill gree actually starts to restore lost accounts.
So gree should be able to restore your old account just like in the old days when you send in a ticket although the reply I got from support I need to read again because I'm not sure.
For those that lost accounts, what version of IOS were you running?