Incorrect date in folders

When I copy and paste a folder, the date of the new folder is the same as the copied folder.

If I rename the new folder the original date remains.

e,g.
I copied a folder dated 14/04/2012 when I pasted that folder the date of the new folder remains as 14/04/2012
I tried renaming the folder to see if the date updated to todays date but it remained as 14/04/2012

If I create a new folder then it is created with todays date.

Has anyone any ideas how I can get a copied folder to update the date correctly.

Many thanks

John