This is happening because your machines have the same Device IDs. This can pretty much only happen if someone include the LANDesk agent in their OS image.
First don't remove the duplicate settings.
Second, check your OS Image. I bet the agent is on it. You should not have the agent on the image. LANDesk automatically installs the agent on an OS Deployment task using Sysprep's GUIRunOnce settings.
Third, configure both types of Duplicate device detection. Under Configure | Services | Inventory there are two buttons an both need to be configured.
Click the Devices button and set it to MAC address match and click ok.
Click the Device ID button and make sure that Reject Duplicate Identities is checked. Make sure that Computer.Device Name and Computer.Network.NIC Address are the only values in there and that Identity attributes to change is set to 2. If you want to really base it on MAC address, only use the Computer.Network.NIC Address and set the Identity attributes to change is set to 1.
Now any machine that has a duplicate will be told to regenerate a new Device ID and the scan will not go into the database. Then the next time it scans it will use the new device ID and the scan will go into the database without overwriting other devices.