An interesting phenomenon I didn't know about. So I had to experiment a little bit in my Excel 2000. It might very well work otherwise in higher versions (XP, 2003, 2007), I just didn't try.
Copying of formulas only works in the same instance of Excel. It doensn't work between different instances. You don't see the difference in the taskbar, but you can see it in the Window command in the menubar. A workmap is open in the same instance as another workmap if they are mentioned happily together as open windows there. And they are open in different instances if you don't see them mentioned together.
So:
- In your source workbook use File>Open to open the target workbook, it will open in the same instance and you can copy/paste formulas.
- If you open the target workbook by clicking on it in Explorer, or after running a different instance of Excel from Start>Programs or an icon on your desktop, you can't copy formulas.
All I can say: that's the way it's designed.
Kees
When I try to copy an excel spreadsheet and paste the whole thing to a new blank excel document the contents are pasted but the formulas in the cells are not there. Would appreciate any tips on how to do this so formulas are included.

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic