Currently, the Constituent filter in Receipts also filters out gifts that were given prior to the constituent code start date, regardless of the the gift date criteria on the General tab.
In my case, if someone came on staff during last calendar year, but gave a gift before prior to their staff constituent code date from, then only the gifts given after the constituent code start date are included in the receipt run. This resulted in two receipts printing for those who I had filtered on constituent code.