are you going to edit>capture image to clipboard in nandub or are you hitting ctrl+1?
I've never experienced this issue, well except for when i didn't press the keys properally
Ctrl+1, paste into your image doohickey, scroll along in nandub (hold shift while scrolling to go through keyframes), then hit ctrl+1 again.
If that's not working, physically go through edit and then hit the copy to clipboard thing at the bottom.