On a site I help administer, we are seeing a peculiar behavior. It deals with searches on people, rather than content.

Of course, on most site pages, there is a site search control. If I use that control, set the search to search for people, and then type as my search term a department name, I get back a list of all the people currently in the department - just as I would expect.

If I go into a site's people and groups, then select New User, I get a SharePoint Add Users Page. the first control on the page is a people editor/picker type control, where I can either type in people's names, or pop open an add people and groups browse window to search for one or more people to select.

So I click on browse, type in the department name, and click on search.

The result list I get is peculiar. It contains some of the users of the department. It includes some people who have been gone for 2 or more years. It is missing some people who have been here for many years.

If I type the name of one the missing people into the search term control and click on search, that person is found with the department name that was entered before.

So, why would the first search give me all the people, but the second search give me some of the same names, other names that were not in the first search, and be missing some of the names that were in the first search?