You are allowed to enter up to four IP numbers per host name. If there is a conflict for at least one IP number, Linuxconf will present you with a dialog, showing you each IP number and the suggested update mode. Linuxconf may or may not update the reverse mapping associated with each IP number.
The dialog appears with a checkbox for each IP number. Those with a conflict, have unchecked checkboxes. This means that if you simply "accept" the dialog as is, Linuxconf won't update the reverse mapping of the IP numbers where there is a conflict.
By checking or unchecking the checkbox, you effectively tell linuxconf to update, or leave unchanged, the reverse lookup for the given IP.