I'm curious why you would want the same attachments? Wouldn't the dates on the bill/receipt/statement be different for the copied transaction than on the original? From that standpoint, it seems to me that Quicken is acting correctly, though I don't know why they would even include them in the copy in the first place making it look like they would be carried through.
I understand your point but it seems like you would want to know what portion of the original order the transaction is for and that the attachment would reflect that subset of the original list and thus be different.
Maybe I'm lucky, but I've never had an order split into different shipments. The other thing is that I don't put attachments in my Quicken data file because of the file size bloat and that the only way to get them out of Quicken is individually.