[DrChiper]

Using calibre 1.26 I noticed that my e-reader did not show a picture. Via the "Check Book" function of the Book Editor, I discovered that the picture was unknown because it was located in a directory "/images/", instead of the expected "/Images/". I tried to solve that via the "Arrange into folders" function which seemed to work as thereafter the "Check Book" function did not reported any problems. So I saved the e-pub, but noticed the picture was still not showing. Opening the epub again with the Book Editor I discovered that the folder was still named "/images", while "Check Book" now reported again that the picture was unknown.

Apparently, the "Arrange into books" function does not actually rename the directory, but "somehow reports success to "Check Book" so the latter refrains from reporting errors until you save/close/re-open the epub.