That's one of the oddities. In the example above, $album[0] actually returns both -- that is, the album number as well as the name (url path actually) of the current album. So, for example, if I am on a sub-album on level down, my tag will link to http://example.com/page/search/tags/TAG_NAME?inalbums=Album#,Album_Name/Sub-album_name,1
(not entirely sure what the '1' is at the end, but is common to all, so I presume it is the gallery root). As I said earlier, the query actually works perfectly on a sub-album.
So effectively, my variable $album[0] is actually outputting an array it seems. However, if I were to echo, say, $album[0][0], $album[0][1], etc. I get nothing whatsoever. Nor do I get anything if I were to echo $album[1], etc...