I imported a 'portrait' orientation photo into a note. The photo was taken on my iPhone directly in Whatsapp then it got automatically saved in my photo stream. It appeared fine in the note itself. (I also resized it, but I don't think that's relevant.)
With the 'Note list view' set to 'Snippet's and 'Note preview' set to show images, the image displayed in the list view is shown the wrong way round. It's rotated 90 degrees anticlockwise.
Doesn't seem to happen with photos that other people have taken that Whatsapp has saved.
Mac version 10.9.10 on a MacBook Air (latest generation). Screenshot included.