I double-click GND in the netlist and pres 'e' and 'w'. The ratnest on GND is still there.
The manual says: A disabled net is treated as if it were not in the net list. This is useful, for example, if you plan to use a ground plane and don't want the ground net showing up in the rat's nest. You can enable/disable individual nets by double-clicking the net name.
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The release notes for the 20060321 snapshot say
"Fixed a bug which prevented disabling nets from the ratsnest"
-Dan