This seems to be a bug present also in the latest PFD update still in Cyan (but it will show Denim when you uncheck PFD). Viewing photos in Lumia Camera in landscape orientation will sometimes not allow a direct transition from left-handed to right-handed landscape orientation. I need to hold my phone in portrait orientation for around 0.5 seconds before the image orients itself. Only then would it allow direct transitions.
Nokia 1520 just updated to Denim and now pictures I have taken in landscape format will only show as portrait even when I rotate the phone. The only way I can view them properly is to edit the picture and rotate it! I think this is a serious problem with Denim..