Optical flow not working on nested clips

Hi,

I am working with some archive footage that contains duplicate frames.  While it was originally recorded at 18 FPS, on Super 8 film, the video was printed at 29.97 FPS, which means that my copy has duplicate frames.  In an attempt to resolve this, and ensure a seamless frame rate, I've cut out each individual frame and nested them together.  I would then like to apply 50% slow motion optical flow to slow it down to a more digestible frame rate, however, optical flow is not working on the nested sequence and the duplicate frames are still there. Any suggestions?

Thanks,

Elliot