When I open Numbers nowadays it appears with the last spreadsheet then after a few seconds that spreadsheet disappears for some seconds and then reappears. Around this time an error message appears which says "Some changes were made to your spreadsheet. The font Calibri is missing. Your text might look different." Until IOS 7 this never happened. The spreadsheet used to open straight away without a problem. That error message only applied if I produced a spreadsheet in Microsoft Excel and copied it to my iPad. But now I get it when the spreadsheet has been nowhere near my home computer. Am I doing something wrong? A similar effect is found in Pages.