How Can I Grant Modification Permission on Work Item creationDate?

We recently upgraded our application from RTC 3 to RTC 4. One of our plugins starting failing when trying to modify the creationDate field in work items. Looking at that attribute, I noticed that it was marked as read-only. I removed the read-only flag. Now some users were getting errors and others weren't when trying to save work items - "you don't have permission to perform the following actions: modify/creationDate".

 Investigating roles and permissions, I could not find a 'creationDate' field listed in the "Permitted actions -> save work item -> modify work item" list (Team Config -> Permissions area). I did find 'createDate' and so granted all users permission to modify this field. However, the same users were still getting the same error when trying to save a work item. I discovered that the users that could modify this field, had full (blanket) modify permissions set for their role.

I believe one of two situations exists here:
 1) the 'createDate' field and 'creationDate' field are the same, but granting individual permission to modify it is not working
2) the 'creationDate' is a hidden field from a permissions point of view, and modification privileges are only granted if a user has blanket modify permission.

I would suspect #2 as being more likely. Perhaps because it is a built-in field that is marked as read-only out of the box.

I would prefer not to have to grant all the users blanket modify permission, so I am looking for a better solution here.

Thanks,
Chris