I mainly wanted to chime in so I would have the opportunity to type AlabamaPamela, which it turns out isn't nearly as much fun to type as it is to say.
In any case, I did want to add that you might want to check your posting setup, to determine if you're configured to use the posting date from the transaction or from the batch. To check, go to Microsoft Dynamics GP >> Tools >> Setup >> Posting >> Posting. (Be careful in this window, as it is easy to make changes unintentionally.)
Once you're in the window, change the Series to Sales and the Originto Sales Transaction Entry (or Receivables Sales Entry or Invoice Entry, depending on which screen you use to enter your invoices).
Then, just check the Posting Date Fromsetting.