Pivot table dropdown number format

I have created a Pivot table with General number format. When I reopened the file all of the numbers in the source data had converted to time. I reformatted the data in the source and the pivot table results but the pivot tables retained the time format in the drop downs where you can select data. Because I was working in whole numbers all of my choices show as 00:00:00. Does anyone know how to reformat the dropdown values without recreating the workbook?