The Aha! "Add filter" automatically updates available selections based on the columns you have chosen as part of your list or table.
This means that if you are on a Features -> list, Reports -> List or the Reports -> Pivot views, the filter options dynamically change. This is because the potential list of filterable data in Aha! is huge and we make it easy to find a filter to yield valuable results. Dynamically populating the filter ensures that only relevant data is available to be filtered at any given time.