This can happen as a result of the way internet networks work. Networks will sometimes retain names of devices that have been connected to the network. So, when a LabQuest name is changed, or when a LabQuest is connected manually using the IP address, the name lookup (also known as reverse DNS) does not always return the expected name of the connected LabQuest.
When the LabQuest is displayed in the Sources list with the wrong name, you will not be able to present it by selecting it from the list. In this situation, you can manually connect to the LabQuest using the appropriate name or IP address. Restarting LabQuest Viewer may be necessary to remove undesired entries in the list.