This is just how QlikView works - if you want a rolling 7 day total or average, your first 6 days will not have a full accumulation, because you told it to EXCLUDE those days by making selections. But there are also ways around it, depending on what you really wanted to display.
For instance, let's say you want the rolling average price of something for 50 days. You might normally write this as avg(Price)/50 and accumulate 50 steps back. But the first 50 days won't actually have the right number. One way to solve the problem is to use rangeavg(above(Price,0,50)). You might have a lot more price variability in the first few days of the date range, but that's legitimate.
I'm sure there's also a way to use set analysis to grab 50 days prior no matter what date range is selected, but then you still have the problem when your set is the whole date range.
Not sure which approach you want. Attached is the example I described.
testRollingAverage.qvw 118.2 K