Grid view Contact List is showing all previous users


Hi, We have a column set as a Contact List. When I click the properties of the column, the Contact List only shows the current users (correct). However, if I click in a cell and scroll through the list, it now shows all users, past and present. Users that are not in the active list of licenses (free or paid). When I click the Select Contacts icon in the bottom left corner of the drop-down list, I am presented with an option of All Contacts, or our company user list. I cannot find anywhere that I can set the default list to be the company user list. Please guide me. Thanks.