I've enabled related images option on NGG, but it doesn't seems to properly works with all posts.
This post, for instance, shows a couple of images:
However, this post is supposed to show at least 9 pictures, since the post has the tag "orchestranike" and 9 pictures have the same tag.
The two pictures displayed are probably taken from some other tags used by both post and pictures.
Another post has the tag "elvis aristide bazongo" and there are 9 pictures with this very same tag, but I don't see a single related image.
Is not a caching problem, as cache is disabled for logged users and anyway I also tried to clear the cache (I'm using WP Super Cache by the way).
Is not a setting problem, as I've set the number of images to show to "0", meaning: unlimited images.