How to see both clips using Effect Controls in Morph Cut?

(2017.1.2 - Win 7 Pro)

Hi--I've searched and searched and not found an answer to this problem, which is driving me crazy.

In the past, when I adjusted a Morph Cut by using the slider in the Effect Controls panel, the Program window would show each clip (A & B) side by side—as I would slide left or right I would see what the frame in each each clip looked like. This was a huge help for me to get proper placement to get the smoothest morph cut.

Now, however, when I slide that slider both windows in the Program window are identical. I can no longer see A/B side by side. I don’t know how this changed or what setting I might have altered.

Thank you in advance for your help.