generating EOGlobalID on EC insertion

I'm running into some weird problems when creating EO primary keys 
immediately on insertion into ECs according to the WikiBook instructions 
here:

http://en.wikibooks.org/wiki/Programming:WebObjects/EOF/Using_EOF/Primary_Keys

I am able to create the EO's PK on EC-insert. If I then push the EO into 
a child EC but before I have called parentEC.saveChanges(), the EO it is 
turned into a fault. Relations that were set using parent EC are not 
available on the EO in the child EC -- I get NPEs when I try to access 
them. If I remove the PK-on-EC-insert code, everything in the child EC 
works fine.

Aside from immediately generating a PK, I don't see anything in the 
WikiBook code that changes the behavior of insertObjectWithGlobalID, but 
it seems like there is some side-effect that is causing this trouble.

Has anybody else encountered this problem, or something similar? Any 
hints on how I might work around it?

TIA,

zak.