Imported hostnames cleared after subnet scan

After I import hostnames into a subnet after an automatic scan some of the hostnames get cleared. 

I can maybe understand the hostnames being cleared that were entered manually into IPAM if the device does not respond to pings.  But on ours it clears them on devices that do respond.  Not only that if you look at the device details by hitting edit the system name is clearly in there but the hostname is now blank. 

Is there some way to stop it from doing this.  If it only works if DNS is available why would you need IPAM in the first place.

Thanks

Jerry