[KevinH]

BTW, just for the record uri's and url's have case insensitive schemes and host names but navigation info after that is recommended to be case sensitive.

Ebook readers and ebook reading software may decide to use either case-sensitive or case-insenstive file systems and there is no way for an epub to know which type of device it is stored on when opened.

Therefore any use of just upper or lower case or a mix of cases to distinguish between files names in an epub is a big mistake on the epub developer's part, as the epub's opf uri and all links are supposed to be case-sensitive.

So I can not just "replace" a "myimage.jpg" with "MyImage.jpg" as the opf manifest url will be incorrect, and img tag urls will be incorrect, etc. This is true on a case-senstiive filesystem as well as a case-insensitive filesystem since the uri's after the host are supposed to be case sensitive.

So although I prevented the reported crash with my last fix, trying to replace an myimage.jpg with a MyImage.jpg will fail in all cases.

The problem only gets worse with buik replacement of mixed case file names.

So again, the best way to handle this situation is to fix filenames inside Sigil before trying to merge two epubs as this is the only way to assure links/uris are properly updated.