When the client connects to a new server, it checks to see if the server is already mounted. It does this by comparing server signatures. The server signature is an identifier which is unique to each server. If no signature is present it will check the server addresses and server names. If the server signature is the same, the client will think that you are trying to log into the same server again and will give you a choice of volumes from the original server.
The server signature is derived from the serial number, so if there is difficulty mounting two servers, check that each server is using a unique serial numbers.
If you are using AppleShare 6.0, 6.1, or 6.1.1, there is an issue which can prevent the server signature from being properly updated. This can come up if you change the serial number on the server, or if you are upgrading with an old User & Groups data file which has an AppleShare 4.x serial number. AppleShare 6.2 addresses this issue.