Hello - if the object is an extrusion it will not, by default, show isocurves.
Same in V5 and V6…
Is that it?
-Pascal
UseExtrusions is the command to switch to making polysurfaces if desired.
(just a reminder )
To stop extrusions being created when possible: Options > Rhino Options > General > Command Behavior > Uncheck “Use extrusions when possible”
Extrusions require less storage space and can result in smaller files. I don’t know of any other advantages of using extrusions over polysurfaces. Unless your project has a very large number of objects which could be extrusions there probably is no appreciable advantage to using extrusions.