Make sure that if you are on your Propects record that you use the Opportunities tab at the bottom of the screen and just double click on your opportunity.
If you are clicking on the Opportunities entity on the Navigation Bar (left side of screen), then you are opening the default group that you have set up in your options.
If you go from the tab at the bottom of the Prospect Detail View, then you are going directly to the ONE opportunity.
Dale Richter