Custom formatting lost due to numbers formatted using Format Cells.
Cause:
This problem occurs because the numbers were formatted using the 'Format Cells...' instead of the 'PivotTable Field...' menu item.
Solution:
Select 'PivotTable Field...' from the 'Data' menu and click 'Number...' in the 'PivotTable Field' dialog box to format the numbers.
1) Select a data field in the PivotTable.
2) Select the 'Data' menu and select 'PivotTable Field...'. (The PivotTable Field dialog box appears.)
3) Click 'Number...'. (The Format Cells dialog box appears.)
4) Select the type of numbering format to use from the 'Category' list box.
NOTE: Depending on the selected category, Excel displays a different sample and, often, offers further formatting options for the category on the right side of the dialog box. For example, when the 'Accounting' category is selected, Excel allows users to specify the decimal places for the number and whether or not to use the dollar sign.
5) Make necessary choices if further options are displayed.
6) Click 'OK' to close the 'Format Cells' dialog box.
7) Click 'OK' to close the PivotTable Field dialog box.
