Comment 1 for bug 566574

This basically boils down to a single issue: pping will only add an RRD file to the rrd_file database table if it needs to create the RRD file on the file system.

If the RRD file already exists on the file system (as it will for a re-seeded IP device), it won't care whether that RRD file is registered in the database. Thus, the rest of NAV doesn't know that this file exists.

A more technical under-the-hood detail is that the rrd_file row still exists, but its foreign key reference to the netbox table has been NULLed since the netbox was deleted.