How to reproduce:
Install a new CMS web site
Log in to the admin UI in N2 and open the upload folder (in our case generated directly under the Root Page)
Upload an image
Create a new content page
Add a tester part (or any part containing an image) to the page
Select the upload folder
Expected result: The uploaded image is showing
 
Actual result: The upload folder is disabled (not expandable/grey) and the image is not showing.
 
Workaround: Upload an image from the edit part dialogue. Now all uploaded images will be visible.