The workbook was not attached. However, usually this happens because of data blending. If there are any values that do not match up in the secondary source (but are in the primary source) it will return a null--in the secondary dimension quick filter. If there are multiple records for one of the members, then it will return an asterisk. There currently is no way to not show these in the quick filter unless the Custom Filter is used (this would be a good one for the Ideas section). Another option, would be to create a 'quick filter' sheet and use it as an action on a dashboard. The following link provides further information on how this can be done:
Hope this helps!