Looks like this is common for the series. Number 4 was just combined (spanish edition with the main record). They like playing with the format of the title and stuff, too. The books I have say "Rin-ne" (in bigger and smaller capital letters font). So RIN-NE, but the size of the letters shows which are meant to be capitalized. This is the series title as well.
Volume 1:
http://www.goodreads.com/book/show/66...
http://www.goodreads.com/book/show/16...
Volumes 2, 3, and 4 are done.
Volume 5:
http://www.goodreads.com/book/show/87...
http://www.goodreads.com/book/show/16...
Volume 6:
http://www.goodreads.com/book/show/11...
http://www.goodreads.com/book/show/16...
Volume 7:
http://www.goodreads.com/book/show/12...
http://www.goodreads.com/book/show/16...
Volume 8:
http://www.goodreads.com/book/show/13...
For some reason this record has the titles caps-locked.
http://www.goodreads.com/book/show/16...
Volume 9:
http://www.goodreads.com/book/show/13...
http://www.goodreads.com/book/show/16...
10 & 11 are good.
Volume 12:
http://www.goodreads.com/book/show/17...
http://www.goodreads.com/book/show/16...
13 is good as well.