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I open two Contact Sheets and arrange them side-by-side. I then drag a single photo from one window to another to move the photo. I can move as many as I like from the original sheet to the other but cannot drag any photo back the other way.I close both Contact Sheets and re-open them and then I can drag the photos back to their original window. Once again you cannot drag them the other way.This happens with both the latest version of PM+ and PM6.
both contact sheets were opened from the Navigator and show contents of the folder. For the instance where I can move a photo from one sheet to the other, both sheet's contents update to reflect the move operation.