The app should zoom to 100% in that case. It depends a little bit on your camera and how it makes embedded JPEGs. The app should start with the embedded JPEG, and then replace it with the RAW once it loads. If you zoom to 100% before the RAW loads, then it might zoom to the size of the embedded rather the RAW. You might need to wait a few seconds until the RAW loads before hitting the space bar. Which camera are you using?
I am seeing this problem when I am viewing JPEG files, not the RAW files
I created a new folder with just one JPEG file in it from this camera and I saw the same issue. If I look at the same JPEG file with RAW Power in my Photos library, the Z key zooms to 100% as expected so this only seems to be an issue with folder browsing.
I am also using the folder browsing interface. What I am seeing is that the zoom level can get “stuck” if you hit the spacebar or Z key too early (so there’s a bug). If I wait a few seconds after going to the image and then hitting the Z key, it seems to zoom properly.