Do you have multiple columns in the document you're copying from? If so, you'll need to create those additional columns in the destination file for it all to show up.
If that isn't the issue, this sounds like an issue we helped someone with a couple months ago and believe it's a 10.6 bug with how we're renaming duplicate attachments. I'd need to see the file to know for sure though. Please send a copy of it to
omnioutliner@omnigroup.com and we'll get this sorted out.