file modification time

[pol <linux_milano@yahoo.it>]

<posted & mailed>

I have noticed that a user can change a file, if he  belongs to 
the same group, to which rw privileges have been set, but he cannot
change its date, using 'touch'.
Is that resul expected?

E.g. User vi-opened a file not owned by him, but belonging to its group,
with permissions:  100664, succesfully exiting with wq.
I have checked that modification date had changed.

As i try 'touch -m 12302007' i get:  'Operation not permitted'

What is wrong?

thank you for you seggestions

--
Pol