The bug is simple but annoying and risky. If I copy a one-frame clip with Rotoscoping effect, the rotoscoping values are not kept when pasting it on the timeline - or even copy-pasting the effect from this one-frame clip to another clip However if its a 2-frame and more clip it works. I had to use a workaround, which was to extend the clip to 2 frame before the copy-pasting, and then shrinking it back to 1 frame.