In Excel 2003 (haven't tested this in 2007):

1. Create a new worksheet
2. Type some text in cell A1
3. Select A1 and B1
4. Right click, format cells, Alignment tab, set the alignment to "Center
Across Selection"
5. Now select cells C1 and D1 -- make sure A1 and B1 are no longer selected
and no text has been typed into C1 or D1.
6. Right click, format cells, Alignment tab, set the alignment to "Center
Across Selection"

The text in A1 is centered over the range A1:D1.

Is this a bug?