Group Contacts list loses group when clicking letters

When viewing a group's contacts, if you click a letter tab to narrow the results, the group filter is lost. This appears to be caused by a missing qfKey.

To replicate:
1. Search for contacts and create a test group
2. Go to Contacts >> Administer groups.
3. Click the Contacts link next to your group.
4. On the results page notice that the page shows the number of results followed by the filter of "Contacts IN <group>"
5. Click any of the letters to refine your results
6. On this results page notice that the URL has an empty qfKey and the filter text after the number of results shows that it is "showing only contacts starting with: <letter>" and that the previous group contraint is lost