Problem with title sort

I have a problem with title sort concerning one specific book (at least I think it's only one book). The Book is "The Crystal City", and title sort won't work as expected, that is, when I press the button, the title sort field stays at "the Crystal City" and does not change to "Crystal City, The" as I expected.

All the other (already existing books stay at "Title, The". Does someone know, what could trigger that strange behavior of one single book?:help:

Thanks in advance, Thomas :thanks: