Jesse,
Here are my notes: http://www.qsl.net/k/kb9mwr//wapr/tcpip/rip44d.html
The endpoints are populated by the RIP routes that are received. You can run the dameon in verbose mode, and periodically check how the route table is being manipulated with the command "route"
As for why you can ping two machines on the same subnet, it sounds like a conflicting route. Again what does "route" show you?
Steve, KB9MWR