Renaming an epub file

Hello,

I renamed and epub file from "L'Essentiel de la grammaire tha.epub" to "L'Essentiel de la grammaire thaï.epub" but when I open Calibre and select that ebook to read it, an extra copy of that ebook is created in the folder with the former name "L'Essentiel de la grammaire tha.epub" (in addition to "L'Essentiel de la grammaire thaï.epub) and this is this copy that is opened.

How can I do t rename an ebook withot having ths problem.

Even if I delete the ebook then reimport it, I have the same problem!

Thanks