Our notebooks (sales people) often leave HQ for more than a week. DHCP server is set up to expire leases after 8 days. What happens is apparent - NB's "steal" IP addresses from each others after some time.
For instance, today NB03 is here, but the Dude indicates NB05 as present.
The reason as I understand it: the Dude takes a device on the map, pings its IP address and doesn't care about what that device really is. If it echoes back, it is lit green. And eventually updates its MAC.

But this is wrong behavior. The MAC should be locked and bound to the device on the map no matter what IP it gets in the future. This way I would always know that what I see today in the network is really NB05 and not another "masked" computer.

Is it possible to set this in the Dude? I cannot find it in the preferences.

You should change device settings.

OK, thank you very much. It was not quite clear for me what that setting meant. Configuring "mac to ip" to all my devices. Is there a way to make it default for newly discovered PCs?

BTW what is the purpose of having the original "ip to mac" as a default?

BTW what is the purpose of having the original "ip to mac" as a default?

2 reasons.
The main reason: you can learn host MAC address only for devices on the same network. Or you can learn MAC address using SNMP from devices which are on the same network whith this hosts. When you do not have such a conditions you can not learn MAC address.
It should be clear for you: The Dude does not checks devices or maps, it checks services (ping, netbios, etc...). When you define device, you only define the "place" where services are located. You can bind service to IP address but not to MAC address.

Well, serious troubles with "MAC lookup: mac to ip".

The device loses its IP address and turns violet. It apparently cannot lookup IP address from the MAC. Reason unknown to me...

Your router(s) will have to have working SNMP and then the dude should be able to retrieve the ARP and resolve the MAC.
But then the dude would have to correlate the MAC table from your various routers to the MAC of the device and then tie the address to the MAC. I really doubted that they had this working correctly... Although it does look like they intended to.

There is a setting on how often to update the MAC table... the Mac Mapping Refresh Interval under Global settings misc. I don't know if this is part of Mac to IP If it is then setting this lower might help/solve the issue BUT Be careful this could overload your network devices!!!