Friends List order changed

I write down every FSS friends activity on a spreadsheet. What gift they sent, what gift they ask, their current Lv etc. My spreadsheet list have an exact order with my friend list at FSS. But sometimes when I check my list at my FSS's friend list they are some order changes. I adjust my spreadsheet list so they have an exact same order. But next time when I open my FSS, the (again) change order. Why????