Hitting browser back button to return to Find Contacts screen retains selected contacts but does not indicate them as selected.

On the Find Contacts screen, select a number of contacts. I'll use 5 in this example.
Select radio button "5 Selected records only"
Choose an option such as "Add to Group".
Hit Go
Hit browser Back button.
Find Contacts screen now shows no contacts selected, and radio button says "0 Selected records only".
Select one of the five previously selected contacts.
Radio button now says "5 Selected records only", but only one contacts is highlighted and checked.
If you now try again to "Add to Group", you'll find that indeed 5 contacts were selected, but only one was shown as selected.