When you add the
template=caption to the shortcode, it means that NGG will use the
gallery-caption.php template in the
nextgen-gallery/views/ directory. Adding 2 instances of
template= might behave funny. I'm not sure which template it will use.
Let's try debug the caption template to start with.
So, change the shortcode back to
[nggallery id=17 template=caption]. Now, what does the code around the link in
gallery-caption.php template look like? Can you post the whole
<a> tag here (don't forget to put it in code tags so it formats for the forum).
If I'm jumping ahead or going too fast let me know, I'm not sure what level WP user you are :)