Lets see what Asrar's feedback has to say about it...
Not being on the same code page is also an attribute of the solution and many unsolved mysteries in SAP.
I think SAP tried to make a few exceptions to transactional CUA intuitive, but that does also create a bit of support type questions when strange things happen.
@ Asrar: Does this explain your problem? Can you provide more details? As an acid test you can run tcode SOUD to check for address data problems between old users and new ones - this is often a symptom.
Cheers,
Julius