Maybe this post by Debra Dalgleish will help....
You can change a registry setting to prevent this from happening (make a
backup copy of the registry first):
1. From the Start button, choose Run
2. Type regedit then click OK
3. Click the + sign to the left of HKEY_CURRENT_USER
4. Open Software, Microsoft, Office, 9.0, Excel, Options
5. Choose Edit>New>DWORD Value
6. Type the name for the DWORD: FontSub
7. Press Enter to complete the renaming
8. Choose Edit>Modify
9. Type 0 as the value, select Decimal, and click OK
10. Close the Registry Editor
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That 9.0 will vary with your version of excel.