Can only change some date format fields to custom format- option to change format grayed-out

Good morning,

I have a number of tabs on a Webi report- I was able to successfully change the date format one tab to yyyy-mm-dd.

For some reason, I do the exact same thing to the other date fields so I can standardize everything, and the Format--> numbers --> DEFAULT is grayed out. Here is a link to the steps I conducted.

http://www8.senado.gov.br/BOE/OpenDocument/1809120828/AnalyticalReporting/help/en/frameset.htm?472204d36e041014910aba7db0e91070.html

Does anyone know why the rest of the tabs do not allow me to change the DEFAULT format for date and are grayed-out? the tabs are being drawn from a mix of universes and Calculation Views directly.

Thank you

Jared