Use of FDC already cancelled stamps

A friend of me asks (in the French speaking philatelic news-group :
fr.rec.philatelie) the following question.

Is it allowed to use a cover, cancelled with a FDC type cancel, later
than the FDC date ?

He gives this example of such a bizarre usage :

url:http://groups.msn.com/_Secure/0QwDdArcUdMwFbUacy93eY*h26w!wiBOMBevYY9VPtNj7RvBkA j72Or4LIQfeEAzu9poc1at*Y6oOUU*HVIz8pK8mgm5vK38iuP9 JJbB1o!0/orchidees.jpg?dc=4675454169905458637

Up to now the answers on frp say this is not allowed as the stamp, once
cancelled, has no more franking value.

Nevertheless, Jean-Paul Droger - who writes here from time to time -
says he received such covers from Romania, Israel and more recently from
Switzerland (with no additional stamp paying the franking nor any
"postage due" (tax).

Do you think this is normal or is it an error from the postal clerk ?

--
All the best,
Pierre Courtiade
(anti-spam address)
to answer me, please replace my 1st name by my last one