To improve performance in the Vuture Contacts page, any lists with a larger number of records than the threshold set in the system will be processed outside the browser.  This means that the processing will occur in the server to free up the browser to load quicker.  Any lists with a number of records below the threshold will load on the browser.

The default threshold for each list is 10.000 records.  If you wish to modify this number, please contact your account manager. They will do so at "Admin.System.AddressBook.Server side paging minimum records threshold"

The only visual difference is that for larger lists the "Select All" button is not available.  You can however, manually select contacts throughout the different pages.