Case Tracker Module - 'Assign to' auto fill field vs radio button selection

Case Tracker Module 6.x-1.x
- when creating a new case... inside the 'Case information' group

The 'Assign to' selection was a field that auto filled (generated a drop down selection box) as letters were typed.
- I must have made a change... it is now a radio button selection displaying all site users.

How do I revert back to the default field?