Removing a format from the book does not remove it from the library

1. I have a mobi ebook
2. which I have converted to epub
3. and then I decided I want to remove it

However, when I removed it, I saw that the epub file was still active in the library.

I didn't get a prompt "Do [I] want to remove the file?", so that is a weird behavior for me.

However, maybe that has an option somewhere to change it? 😕