CDF edits don't 'Stick'

Hi

I am trying to change all the well resistors in a given design to
hi-res poly resistors.  In DFII I select 'Tools,CDF,Edit'
I get a menu and I select my poly-resistor symbol which is no more
than a copy of my well resistor symbol.  I edit the field resType to
be RPHR and change the model to point to the correct simulation model.

I select OK and the menu closes without error or warning.  The
schematic is updates and it simulates with the new model.  I save the
schematic.

If I now close DFII and re-open the schematic all the resistors are
back to well resistors.  Obviously I am missing a crucial step.  Any
help would be appreciated.

JNB