r56918 was deployed, causing entries containing those space characters to become "magically invisible".
See for instance http://es.wikipedia.org/w/index.php?diff=26929574&redirect=no
Looks like on September cleanupTitles.php was run after that revision, and indeed seems to have worked for other wikis (eg. it's unlikely that enwiki didn't have any nbsp-ed title) but at least for eswiki it didn't correctly process the titles.
So a global pass seems advisable.