Spurious ratlines in PCB

PCB seems to be drawing spurious Rat lines for connections that are not in the net list. In particular, I have a pair of 34-pin headers and each shows a connection between pin 2 and pin 28 of the same header. There is a signal routed to pin 2, but pin 28 is a no-connect. The Net List window in PCB shows no corrosponding connections, and the *.net file created by gsch2pcb likewise shows no such connection.

This is NOT a case of a pair of pins that appear to be connected by a rat line going elsewhere. The auto-router will place a connection where the bogus rat line indicates.

I have re-run gsch2pcb and re-loaded the netlist and the bogus rat line re-appears. Prior to re-running gsch2pcb, I added a ground connection previously omitted, and it DID show up upon re-loading netlist, so I know the tool flow is good.

I am using version 20060822 with Fedora 6, PCB was installed via yum.

Is there some error I am making that would cause PCB to draw a rat line for a connection not in netlist?

Thanks,
Samcat