If a want to create more than one node gallery the "Upload New Items" tab is only shown for the latest node gallery relationship I have created.
E.g. I have a node gallery for the tow content type pairs:
media_album with media_album_image
user_album with user_album_image
I have created relationships for both galleries. However only the latest created relationship seems to work for uploading images, i.e. shown "Upload New Items" tab on the full node.