When copying and pasting an unpublished page the new page is created successfully but without the contents of any "XHTML string (>255)" properties. This issue does not affect published pages.
I found that this bug has already been reported and supposedly solved (http://world.episerver.com/Support/Bug-list-beta/bug/34761/) but it's affecting the 6R2 site that I'm working on.
Does anyone have any ideas why this might be?
I do not think you are experiencing the same bug as in the link you are refering to?
The bug in the link is for copying pageTYPES and not pages as you do.
This is reported bug 76999 (Copy function copies only basic fields for unpublished pages) and was closed with reason As Designed. There is however a comment that the functionality has been rewritten to support copy/paste for CMS7.
Can also add that the bug cant be found in the buglist since it was closed As Designed.